Check the Bargain Finder, as suggested, as I once found base rock for sale in it. Your other option is to buy a box from J&L and sell the extra. There's a fair demand for base rock. I might even be interested.

Jess,

I got a few fairly large pieces i'm looking to sell.
PM me and we'll go from there...

I have some base rock as well. If you can't get some from ungp just let me know. This is rock from J&L.

Keith

I've got my base rock, thanks for the offers though guys. Richer had a bunch of it and sold it all to me for a very very good price. So I've got quite a lot of base rock in the tank, now I'm looking for live rock.