H - the Fox parts factory doesn't have any spare parts. Been looking on the auction site for Fox carbs and am coming up empty. I need to .312" carbs for my Twin and I need one for my .46BBRC. The 50BB has an MkX .330" carb on it which might be a bit large for its rev range too.
The MkX carbs are good carbs, this old one has just seen better days. I'll mess with the detents and put some Teflon tape on the needles threads. Should clear up most of the touchy needle problem. The biggest problem with these carbs (MkX) is the coarse threads on the needles.