Dan's got some pistons and rings on his site. Cheaper than Honda dealers.
http://www.geckomotorcycles.co.uk/index.php?act=viewCat&catId=25

Gavin at Jap4 sells Tyga stuff in the UK.
http://www.jap4performance.com/

I use David Silver for Honda parts too.
http://www.davidsilverspares.co.uk/

As mentioned earlier, Andy sells Hel brake lines at a good rate from this site.
http://nsr-world.com/marketplace/