Several things would have to happen in order to participate in non-US countries. I haven't thought of them all, but the main one is this:
Real, trackable shipping which is through EMS/Global Express Guaranteed, which means it would cost $100-200 to ship outside the US to Europe (I'm getting quotes from pirate ship for priority express international and UPS and quotes from USPS for EMS/GEG).
- note: the weight of the boxes that I have participated in vary from 9-12 pounds
- it would be the same requirement from the international location to the US location
- the customs # would be insufficient
However, if those outside the US wish to participate, they can always designate a US proxy and send a selection of pins to that proxy (OEs, LEs, LRs) so that once it's their turn, the proxy & them can discuss which pin(s) to trade...