When I was workin on my head, I had to borrow a friend's valve spring compressor; it was the one that's used when the head is off (huge-honkin C-clamp that goes under the head and pushes down on a valve, and the other piece over the valve retainer)

I would like to have one that can remove a spring w/ the head still on the block, but every one I've tried is simply too big to fit down to the bottom of the valve seats!

Where can I buy one that's slim enough to fit down in the head?