I believe these machines use the flat twin 18HP Briggs I/C engines. There are a lot of those motors out there so finding one at a decent price shouldn't be too hard. If you're looking for bearings and seals for your gear box, many 6x6World members including myself go through Buffalo Bearing because they give you really good prices and can find odd ball parts that other places can't.

1 800-669-8019 or (716) 874-1720

Tell them the guys from 6x6World referred you to them and they'll take good care of you.