The 212MBE is 4ohms. Can't run it with the MB210. The only option really is the 210MBE if you want to stay in the MB line of GK products.
There are GK 115 8ohm cabs on GC.com
I just looked on GC and you are right about the 2x12 cab being 4 ohms, not that I questioned you. I didn't look at the specs of it so I missed the 4 ohms. In the description it says it would be good to use with the MB210. They need to change that in the description. In your opinion which 15" cab would be a close match as far as dimensions?
I haven't stacked before so do you think another 2x10 would be good or should a 15" be stacked? Thanks.