I got mine in my local elcetronics store. Maplins. Kemo is the brand name on the kit.
However you dont need to buy it as a kit. You can but the stuff seperately (I dare say it would be cheaper.)
The kit I used had...
A plastic tray
A pair of plastic tweezers (it has to be plastic, the etching solution is highly corrosive to metal)
A sachet of developer
A sachet of Etching Solution.
A selection of 3 PCB boards (one photoresist, one double sided, one single sided)
I bought an extra photoresist board, which I split in three. Two for PCB,s one as a test strip.
There are loads of tutorials on the web.. Google diy photoresist pcb. you will get instructions on how to do it. Some mention making your own photoresist layer. i dont see much point in that if your doing a one off. Pre-prepared photoresist boards dont cost much more than standard boards. Then you get a probably better board with less hassle.
Just one of many tutorials