You can pick your friends and you can pick your nose, but rarely can you pick your friends nose
Maybe find a couple of board members you think are trustworthy and try to get them on the trail.
Sticky situation though, do you front them $$ and wait for them to find the part - or - do you hope they find the part, and if they do, say at a car show swap meet, they have to front the money for your part so someone else doesn't buy it in the meantime. Then they have to hope to be reimbursed by you...
Don't be to harsh on your brother though. If I went to Austrailia, and my brother wanted me to find some obscure Austrailian thing, like , say, a Wilcox Co. sheep shearing blade from 1952... yeah I'd look for it in the course of my vacation or business, but I wouldn't "waste" days on end searching for it when I could be drinking VB or Tooheys and getting a sun-tan.