Do you mean the cast steel version fitted to earlier A2’s ?
If so there are loads on eBay for £2 a boot but the quality is crap as they need replacing every 2 years as they crack
Only other suggestion is buy the joint for the pressed steel arm and use its boot
I’ve been through my eBay buying history but can’t find them. I remember buying something like 12 and put them away I. A black plastic bag with talcum powered on them and sealed the bag
Do an eBay search with the size something will come up