Toto Drake II has 1-9/16 from wall for baseboard etc. Not the same as the tank, but not enough for your baseboard heater.
Think you misread the OP's need for more than 3".
I don't know Toto's line well enough to pick one...it would take some careful study of the catalog, if it exists. Toto tries to make all of their trapways nice and smooth arches, and that makes it tougher to have a large gap in that location. Don't give up, someone may have researched this and know, but it's probably time to start looking over tech data sheets.
An alternative would be to use a 10" rough-in toilet which would move it out an extra 2" verses where their spec sheet says with your 12" rough-in. That would also mean there's more gap behind the tank, but other than that, has no operational effect.