I'll try out a 12" one in carbide let me know the price. You want carbide if you want them to last. Specify the top bearing, and diameter of the top of the bit, to be 1/2" (the 1/2" bearing is a standard size) - specify the depth of cut to be 2". I can send you a schematic drawing if you like.
The guy who made mine is now on disability (damn cancer). When he made mine originally, I gave him a list that included 9.5", 10" and 12" then later I told him to drop the 10" - but bymistakely he dropped the 12"...so I'm in need of a 12".
When he made these, he machined the shafts and the blades separately, then made a jig to attach the blades to the shaft so that the two flutes were exactly the same distance from the shaft (otherwise the thing would chatter like hell).