http://www.wiggle.co.uk/sram-pg950-9-speed-cassette/
bottom of the page has the chain and tool if you don't already have one.
Order from wiggle and it'll be here in a day or 2 provided its in stock currently.
I've got the tool though it you wanna save buying one, you could come round at the weekend for it fitting.
Need to plan it in though cos the little man dictates my movements this weekend, wifes off holiday shopping.