Jim- Welcome to iRV2, and the Alpine Forum.
IIRC the Avalanche has a rear radiator, not the standard side unit in the Limited, Apex & SE coaches. It is likely a match to one used by Freightliner, Monaco or other rear radiator coaches. If you belong to ACA, you can email Mark Harrah to see what he can recollect from his resources. I'm guessing it was supplied by Radiator Specialties of Sacramento (google).
Worst case, you can take the radiator out and have it copied by a shop in your neck of the woods. From your locale, I'd guess there is a radiator supplier used by Monaco and probably Winnie in the very general vicinity of Elkhart IN that can whip up a substitute.
FYI, you can use the UserCP feature in upper left of the screen to add a custom signature to show your coach's year, make, model, options, family history, pets, current ailments and medications, shoe size, tax bracket, and other pertinent information so folks can gauge the applicability of their experience in responding to your queries here. (I was kidding about some of the above, no reason to post your shoe size).
Again, welcome aboard. There is a wealth of info here.
added on edit: You can also do a Search from the Alpine Forum page on "Avalanche radiator" and perhaps send a private message to other Avalanche owners to see what solved their radiator issues, then post useful results here for posterity. I get 6 or so threads that mention both Avalanche and radiator, tho most of the discussion is about the side radiator.
Baja-tested '08 2-slide 36'
Alpine: The Ultimate DIY'er Project