Get it from
http://www.sidewindercomputers.com - tell him Steve sent ya
I buy from Gary all the time (I'm in Cardiff). He's a great guy, does his best to fulfill your (ahem!) every need and shipping prices are MINISCULE! I paid £2.50 for my MCP600 Rev 2 impeller (free) the other week
When I bought the actual pump from him I think it was a fiver. That gives you some idea of the costs