Good luck with that. Ya gotta think it's pretty slim chances anyone who already owns a
B21 with the 3pt is likely to put his hitch arms up for sale on ebay. I'd think a good place to check would be tractor salvage or construction salvage yards. The
B20-21 TLB's have been around for quite a while and some have no doubt made their way to the junkyard. Also, you might find a contractor with a
B20-21 who has the arms and never uses them. Sorry to say that besides paying through the nose for new ones, it may take luck and persistence to find something affordable.