I would post in the "Want to buy" section here, post an ad in your local Craigslist and check Fleabay and Reverb.com. I have seen some post-market dyna snare frames but I don't know enough about them to be helpful.

There are about four different style snare frames from different years of manufacture.Most will fit and work correctly on all Dynas,but you may want to be period correct with your frame.There is a thread on here somewhere that has already discussed this topic so you may want to search it out using the search button on the forum.

Wayne