I believe estwing is probably your best bet on rock hammers.  Most hardware stores do not carry geological hammers in stock, although they may order them for you if you asked.  Also, what type of rock hammer are you looking for?  I had to order my hammers online myself.  In my opinion, if there was one hammer you should always have in your inventory it's a crack hammer.  It will be the most versatile and useful.  (example:  http://www.estwing.com/g_crack_hammers.php)

You will be able to split small boulders without a chisel, you will be able to split larger boulders with a chisel, and it will last forever.  I used to use the normal rock pick hammers (example: http://www.estwing.com/g_rock_pick_long_handle.php)  But the pick end will eventually wear out or even break off and you will have to re-sharpen it and eventually buy a new one.  Also, there's just not enough weight behind those pick hammers to really get much work done on their own.  I think a crack hammer an chisel(s) will be much more effective for any hard rock mining.  The only down side is that you have to bring two tools with you instead of one, but I sincerely believe that the benefit outweighs the cost.  I saw an Estwing crack hammer on ebay you could snag if you want.  http://www.ebay.com/itm/Vintage-Estwing-No-83-4-lb-Nylon-Handle-Metal-Head-Mallet-Hammer-/390638001156?pt=LH_DefaultDomain_0&hash=item5af3d6dc04

Happy hammer hunting.   

Scott

Heck yeah, Tim. I don't see what's so great about the pointy end
on those so called "rock hammers" anyway. Never owned one.
I've always used the flat tapered-end brick hammers you can
find at any Lowes or Home Depot. Most come with a Lifetime
warranty these days in case you break it.

And the hammer on the left in the pic below is a "crack" hammer
also from Lowes or Home Depot. I recommend atleast a 4 lb
crack hammer.
The 3 pounders just don't have enough heft. I think they make them for girls,
but I could be wrong about that.

Chisels I buy at the flea-market. Go out and rummage thru the bottom
of some old tool boxes and pull out the chisels. I don't think
I've paid more than a dollar for a chisel in years.

Happy Hunting,
Joe