Lyman and RCBS (and I'm sure there are others) will build you pretty much any mold you want. Just give them the dementions.
I never thought of it, and I dont think its gonna get on my "to-do" list, but if you want one, by all means call one of the mold makers and go for it.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071