Jerry,
I don't know of an off-the-rack gun for you. I think there's some level of custom in your requirement; a specially ordered gun (from one of the Spanish makeres maybe), a restocking of the butt, or conversion to straight grip. For the latter option, the gun will have to have enough wood on the bottom behind the grip (see Shotgun Technicana). Usually the target guns have big fat stocks and can be modified.