Gents, I've just been to book my 650 in for the valve check.
I mentioned to the man that I've heard there is a shortage of shims about at the moment but he said "That depends on if you want OEM or aftermarket". He has got a ready supply of shims on site but they won't we Suzuki, he says they will be just as good and I have no real reason not to believe him, as he has done me proud for many years on many bikes.
However I would like a second opinion from anyone who cares to give one, particularly if you've fitted aftermarket. (I think I read someone did recently?)
This is of course if new shims are required, but I have told him if they're real close to the limit then get them into the middle of the tolerance.