Need to terminate 12 RG6 cables. The largest splitter available is an 8. How do I do it?

Just feed another splitter from one of the output ports of the first splitter. I prefer to split the feed into two with a two-way splitter, then feed two 6/8 port units. You'll probably need an amplifier to drive that many cable runs though.

I have seen cable amps with a bunch of outputs in condos.

Here is a 16 port splitter. http://www.mjsales.net/items.asp?FamilyID=220&this_Cat1ID=265&Cat2ID=93
I agree that an amp may be required.