Any Evinrude Simplex or Johnson Ship Master 2-handle box will work, including the "old" models from the 1950's to the "new" models thru the 1980's. They don't make that type any more. You will need cables specific to those boxes, but they are still available. You will also need a set of cable brackets and bolts to mount on your engine, and OMC-type cable end fittings. You can probably find all that on EBay as well.
EBay has a number of sets with cables and ends in the $165 range. If you can find one with the right length cables that will save you an extra $100.