Ouch. I'm gonna assume it was a pto length issue, or other operator error, since you aren't concerned about a warrenty claim. We've all been there, how a person learns, but just heading off the inevitable line of qurestions you'll get...
You'd have to search through the industrial supply places to find the same housing. Obviously JD buys these gearboxes from some gearbox company, but typically they try to have an exclusive on them and keep the relationship from the public. That way they can do a 50-100% marhup on the replacement parts. (Actually JD buys the tillers wholesale from some manufaturer, and the tiller maker buys the gearcases wholesale from some gearcase making company, so you can try to figure out similar tiller brandnames, or the gearcase co to begin with....)
So, the chore is to figure out what gearbox manufaturer you need to get it from, and then find a retailer that can get the part from the wholesale gearcase company.
Sometimes more hassle than it's worth.
Hopefully someone here can tell you who makes the tillers for JD, and see what other brandnames get tillers from that same company, and you can look to those other brands. The Fronteer line esp, will end up being a Woods or Brady or some such painted green....
Man that bottom pic gives new meaning to 'tore it a new one' doesn't it? Ouch.
Welcome to the forum.
Edit: This thread might give some leads:
http://www.tractorbynet.com/forums/attachments/194024-john-deere-frontier-tiller-info-2.html
--->Paul