Many LT tires will work, Cooper has these... IIRC they are E rated and 10 ply or something. The ones I bought were off brand, made by Cooper, and used the exact same tread as the Cooper branded version. I got them at the Cooper dealer even.
16.5" will be your issue, could you swap the rims to a 16" that is more common? IIRC 16.5" doesn't have the safety bead. That could affect you when airing down.
EDIT: I did not see the post above that you already got new rims.