ugh. why!? auto is much more reliable than the equivilent manual.. have you sourced a box yet!? You would be better off buying a wreck if you havent, and stripping and replacing as you go.. that would be MY sugestion as to how to go about it.. It shouldnt be very difficult.. the more complete the donor car.. the better
Other option seems to be a supra box.. but im thinking that would require some adaptor plate to be made up and a bit more thinking out side the ryobi square..
search!