What I'm after is a compressor (preferably electrical) that I can marry up to a reservoir I got for free. So just the top part. Bit of an odd one I know but I thought I'd put it up on the off chance!

Can you not buy a nice cheap compressor and mate the two reservoirs so you have twice the capacity?

Machine Mart Click Click

I have to say tegwin that idea didn't occur to me, but now you've said it it's tempting!
Cheers for the links ashg