I've been to all three Amoebas (others on Haight in SF, on Sunset in LA) and while this one is the original, it is sadly the smallest. However, this makes it cozy and less crowded. If you can't find it here, either in the new section, the newly arrived used section, the used section, or the clearance section, ask a staff member. There are nebulous categories (downtempo, dance, electronica) and the staggering selection can be overwhelming. There is also stuff stored below the bins, so you can be there for days.
The used section is a treasure trove of out of print, import, and singles treasures for very reasonable prices. But no bootlegs here.
Go to Amoeba. Now. If they don't have it, then go down Telegraph one block towards campus to Rasputin (which is sometimes cheaper for sales on new albums and often has cheaper used albums). If it's a new release and they don't have it either, I guess you can go to Tower (down another Telegraph block and up Durant).