Here's a reposting of my original 2/28/2012 message. I recommend really good walking shoes of you're on this circuit.
So lets start with some very easy places to find them. Many of the employees inside of the Main Street emporium have lanyards or hip pads for trading. You can also find a trading board at the check out counter in the corner of the building as you exit out to the town square. Employees inside the Mr Lincoln theater waiting area often have lanyards
Moving towars the park center, lets go clockwise into Adventureland. You can typically find a lanyard or two in the trading post. They're often behind the counters so you may have to be friendly and ask. You an typically find another over by the enterance to Indiana Jones.
Heading into New Orleans square, be on the look out for the janatorial staff - while not all of them have pins, you might be surprized. Into the square, you have Le Bat et Le Belle - hit/miss, but you also have the pin shop in that district - its often behind the counter as they're a little short handed in that one person store. Don't forget to check the other shops.
Moving towards Critter country, I've never had much luck unless I catch the occasional cast member walking by. But DO check out the country store.
Coming back out, very past Big Thunder mountain and take the back trail to Toon Town and Small World. Petting zoo has often had pins available when I've been there. Shop in Toon town has also had a few pins. Hit up the stroller attendents as you go by Small world. The toy store and film keosk and souvenier stands all have lanyards when I've been by. Poor person stuck selling "film" will likely appreciate some company.
Heading towards the Matterhorn, you have another hat shop - pins occasionally. The walk into Tomorrowland is usually pin "Death Valley". Normally just a Materhorn line queue and not an attraction in sight. Endure and pop out by the Submarines. In addition to finding Nemo, you'll find a very greatful stroller attendent who usually has lanyards or will know people who do. Some of the exit crowd by Autotopia will have some. Hat shop hidden beneath the kinetic sculpture usually has a lanyard behind the counter. Never had much luck getting pins from Asimo - Innoventions, nor space mountain. But the Captain Eo attendents had a lanyard or two. (Even got in to see the show too). Coming out you're at the Star Tours exist - go inside my Pin Padawan. Search out the old arcade - cast member there be ... pins have they. Moving into the main store, you can find another board behind the corner check out counter. Lanyards have they behind counter search your feelings (or for ones sewing names on hats). March right across to LGM command and pin central. But beware - outside await a wretched collection of ruffians and villianery. You must be careful. Inside of LGM at least one employee will have the treasured lanyard and maybe one or two more behind the counter.
Putting tomorrow behind you, move back into the center of the square. The stroller attendent for Pixie hollow may have a pin or two (was a child's lanyard when I was there). Fantasyland becons, but the fantasy is that you'll find many pins there - too crowded but you never know. And rumors persist that you can find castmembers with hippads of pins to trade.
By now you're likely in the mood for a parade, and what luck they're setting up for one. Lead the parade and work your way towards the main enterance (going from Small World to Main Street, trading all the way - look for the Disney Castmembers manning the ropes. And ESPECIALLY keep an eye out for their mangement staff -- hitting them when they first appear is like being Jack Sparrow falling on a Spanish Treasure Galleon. They may take refuge in the art shops but you can track them down before they get away.
Take in the show if you want, otherwise escape to the Frontier(land). There you'll find Westward Ho (check behind the desk). And if ya be a friendly type, trade with your fellow pin green horns... they'll have fresh untouched genuine AAA/Costco/DisneyTravel pins and be right eager to trade with you. Cast members on duty often have locked lanyards. And those starter pins trade just fine with the rest of the cast members in the park. You might even make a new friend too.
Moving over to Disney California Adventure, I'll just give you some quick hot spots. The entire traffic control castmembers as you walk around CA Soaring into the park. Hit the DCA welcome booth and then turn right towards the water ride. The country store / Disney Vacation have pins, as does the UP challenge course. Mermaids like pins -- at least some of the line monitors do. The store near Ariel's grotto may also have a lanyard. DCA has a pin death valley as you go past the games and the remains of the Maliboomer. But they claim there were going to put something back there... Boudine's has pins as did the old Tortea factory. Not much luck in Bugs Life. But the ride attendents / stroller parkers over by Tower of Terror and the Hyperion theatre often do. Check out the Animation station as they usually have a lanyard or two. And then there is the main store and their central pin collection. The smaller Tron themed shop had a lanyard too.
Hop back over to Disneyland and you're likely in time to work the parade route going the other direction - and hit the reloaded castmembers too. If you left a positive impression, they may even have a treasure or two for you. (First of newly released hidden mickeys anyone? A cast member exclusive pin and even a DSF LE300)
And if you're tired of the park, you still have 3 hotels worth of gift shops and cast members to search. Did I mention the occaional greaters at World of Disney
Won't vouch for the "quality" of the pins, but I've usually not had any problem finding solid quality open editions, the occasional "genuine" hidden mickey and a treasure or two