I'm not a movement expert, so I can't give an informed opinion from a service/repair perspective. But you're right that the 61GS can pose some problems in that regard, for example finding a main spring. That said, I'm a big fan of the 61GS. It's a true hi beat movement (36000) and it is a pleasure watching the smooth second hand going round. The only other true hi beat GS is the 45, giving you the choice between hand wound (45) and automatic (61). The 45GS has a rich history, but in my personal opinion the 61GS in it's many variations looks a bit more refined in design than the 45GS (in looks that is, I can't give an opinion on movement quality). My favourite GS is probably the 6146-8000 with the cross hair dial:
I use fromjapan as a proxy for buying. They take care of customs forms etc. and offer several shipping options. I tend to favour DHL Express, because they offer the option to pay import duties while the watch is on it's way, so it never gets stuck in customs. With Fedex International sometimes that option is offered too, and sometimes I get an invoice by mail some time after receiving my package.
So the process is pretty much: bid on and buy what you want through their site, wait for it to show up at their holding facility where they hold it for you for up to 6 weeks or 60 days (I'm not sure), select what you want shipped and what carrier to use, wait a few days and receive your package. It's always worked pretty much flawlessly for me so far. Something like Buyee will probably be the same.