I wouldnt say there rare but there not exactly common. £10 for a 2" fish seems a bit on the high side for me but then if theres no where ese near you that sells them its a fair enough price.
My LFS sells 2" T Bars at £5or6 each and they're locally (or UK, can't remember) bred ones. I've only ever seen them in this one shop and I regularly visit 3 shops. I wouldn't call them rare though - probably uncommon, there's a lot rarer out there that I've seen.