there are no commercial gpu blocks for the 7950 yet, probably because there is no demand, but a few companies are working on watercooling solutions
my 2 cents: there won't ever be a good waterblock for the 7950 because the top watercooling companies won't bother designing such a unique block for such a short lived card. so you'll be suck with small tubing, alu constructed POS waterblocks that asus makes.