I got them from Technobots:

http://www.technobotsonline.com/csk-hea ... 32995.html

Pretty cheap, you can get almost 200 for £5. But they are quite soft and will dislike you if you try to attack them with anything other than a pozi-3 bit. I'm looking at getting the same size but with socket heads for the Drumroll II chassis rebuild and for continuing the work on Carcinus.

Found 100 on eBay for £9 so a bit more expensive but they're a higher grade so should be a bit tougher:

http://cgi.ebay.co.uk/M6-X-30-COUNTERSU ... 1047wt_905