I went here first: http://www.skatebristolshop.co.uk/suregrip-cushions-super-535-6295-p.asp

Cheap postage however they fucked up and I only got 5 and then they ran out of stock so I got a full refund and got to keep the cushions =]
I think they're the cheapest but best send them a text or email to see if they're in stock!

I tried ebay after and bought a half set fairly cheap - just ask for combined postage if you have to buy the barrels and conicals separately!