I have not looked for an online dealer as it is so easy to buy locally. If I wanted to buy online I would get the Clearkote clay bar from http://www.seriousperformance.co.uk/sp/products/maintenance.php I would highly recommend Alex from Serious Performance
I liked the Sonus bar available from Autopia. It was very gentle but effective. I used the Sonus Glyde lube with it. If you go this route I would wash before using any polish or wax. There's some serious suds in the Glyde lube!