Tim, have you tried Outdoor Distributors?
I have an old (circa 1973) True Value garden tiller that I've been able to find parts for through their website. (My tiller cross-references to an MTD, I believe.)
I took a quick look at the Outdoor Distributors website, and that "785" prefix in your model number comes up as being manufactured by "General Power".
I didn't dig further on the website for your part number, but it may be worth giving them a call.
FYI: I haven't used my tiller since last summer, but it started on the second pull yesterday! (It usually starts on the first, so one of us is getting old...)