Anyone got a second hand 7 speed rear mech for a MTB I can buy in their box of old cycling bits? Can be as acky as you like (as long as it works) as the bike it's going on is acky.
You probably know this, but in case anyone reading doesn't and has one in their bits box, any 7-8-9 speed mech should work as the indexing is in the shifter not the mech.
8 speed is probably better than 7 though due to chain width/jockey wheel issues.