I picked up a can of #4 at my local TAP for about $12 for a pint. The stuff is water thin too so you prob wont need much. I dont remember if they had smaller cans.
If you're out in Elk Grove, let me know. I think I even have one of those syringe applicators they recommend for it.
EDIT: Just saw your post about sump design. If you're thinking about building a sump, be careful to calculate all the costs, including necessary tools.
I bought the Weld-On so I could build my sump. Since I didnt have many tools, the cost to complete the job wasnt worth it when compared to a glass 20L or 30 from Petsmart or something.