It depends what you are actually looking for of course. I've bought from a few folks in Europe, and there are a few others in addition to the ones already mentioned here in North America - I recently bought some NOS bits from an outfit called
Flying Squirrelin Toronto for example - fast service, and no issues with my order. And just for info - the one time I bought from PM the price was OK and delivery was fast, but I notice he ( and many others) is often selling things at a premium that are still available directly from Suzuki
In Europe, I've bought from
Erik in The Netherlands. Another NL supplier I've talked to, but not yet bought from is
here.
Crooks in the UK often has things, and Reiner in Germany also seems to have a lot of GT750 specific items. I've listed a few on my web site
here and other reference pages are
here and
here.
Happy hunting !