The GMN I got were a set of vintage 90s zz ones with the metal shields and then a newer set of 2rs ones. They seemed to be identical other than the shields. The old GMN I got from a vintage skate gear seller.
The FAG and newer GMN I sourced from a guy on ebay in the czech republic. They're really hard to find at a reasonable price in the US, most places sell them as singles or in bulk so a set of 8 was as much as just buying swiss 6 at that point. Took like a month and a half to get them as he had to order them from the factory first then ship them to me.
The biggest issue I see with them is that they're not designed for skating, so they're lubed with thick grease that's a pain in the ass to get out (the best way I found was to heat them up so it melts a bit and then use 91% iso alcohol to flush out) and they have brass cages. I couldn't find them with nylon/delrin retainers like you see in purpose built skate bearings, although I'm sure they exist... the GMN catalog is like 1000 pages long. Even still, I have some older Pig bearings with metal cages that are faster than any of the German ones I got so I think it's just down to their intended purpose... they're made to stand up to ridiculous forces and speeds, but they're not necessarily made to spin freely and accelerate quickly like a good skate bearing is.
I had SKF on my list and I think I did source them at one point but I'll have to check my bookmarks. Honestly though, for all the trouble and time I went through I don't think it's worth it... a set of swiss 6 or ceramics from any good manufacturer will probably still be better suited for our purposes or the performance gain would be negligible. Hell, the fastest bearings I've had so far have been a set of Flip HKD 7s that cost about $10 or a set of Modus 7's that were about $20. I'd feel much more confident in buying a set of high end modus titanium or ceramics than I would trying to import a bearing that was never really designed to be used for skating.