From the UK
There are rarely issues here with parts for Japanese bikes except perhaps for the ancient (sorry - classic) models. That said, whenever I have had trouble sourcing a part, I have contacted my Californian dealer friend and he has found them via the USA importers without much trouble. That means that you yanks have the best of a good deal in parts availabilty and they are cheaper there too. Your parts cost approximately 1US $ to our 1 UK £ - that's currently a ratio of 1.6:1 in your favour. To be fair, BMW parts aren't hard to get here either but cost more than their "Jap" equivalent and we're in the EU. The problem here with BMW is that you have to accept that ONLY dealers are allowed to work on your bike at premium rates. Touch it yourself and all warranties and support evaporate and your bike is blacklisted on the "approved" secondhand dealer lists. A recent example I encountered was a guy who fitted higher bars and the longer braided hoses needed. He couldn't bleed them properly, which apparently needed a BMW computer (just to bleed brakes????), so he took it to a BMW dealer. The dealer flat refused to bleed them as the parts were not approved BMW accessories. The only way back on the road was to replace the originals. If it had been mine, the dealer would still be prying it out of his ar**.
Reliability? There is/was a Motorcycle News UK comparison road test on YouTube in which they ran several touring bikes from Lands End to John O'Groats (as far as you can go end to end). All except the BMW that wouldn't start at Land's End and had to be recovered by BMW before the test began. To supply a test bike that fails at the first hurdle says it all. I have run group tours throughout Europe for decades travelling with a very wide spread of makes and models. The make most needing recovery and repair? BMW by a margin of 7:1. Mostly electrical failures though we have had clutch failure on a low miles 1300LT, and a rear drive failure on a GS. Perhaps they have a higher percentage representation in the touring groups; of say 30 bikes, 3-5 might be BMW. That doesn't offset their 7:1 breakdown record.
My life changed, road and racing, when the first CB750s arrived in 1969 and I've never looked back. I once bought a new R90S and it was a nice enough bike though the seat was hard as a board. When I took it to the dealer for a service (not a lot of miles but out of warranty), he announced that the engine shaft seal (behind the clutch) was leaking. "See, you haven't fitted the updated part to fix that problem" he accused, forgetting it was his job to advise me of updates and fixes. "What was the fix?", I asked. "A longer dipstick to reduce oil level"!!!!! So much for teutonic engineering! I vowed that was the last BMW I would own and it was. I have road tested the 1200 GS in a moment of weakness and I thought it was gutless, rattly beast with a ghastly gearbox and that was the latest improved version.
I'm sure that riding a free road test bike for a day or a month can be an enjoyable experience and accounts for the press plaudits but that is not the same as long term OWNERSHIP which is where Japanese bikes score every time in my experience.