I've had 37T pulleys on backorder with Fusion for over a month.
After reminding them on Friday, I have 1 on it's way (I ordered 2)
If you want Durga diff halves, I have a NIP set you can buy, I may have a spare hex or two as well.
501 diff halves are rarer than an honest politician, I got lucky and found a used set.
I'd advise you to get a pair of 18T layshaft pulleys for spares as well, my lad has done a couple of them.