I don’t think you need a replacement frame. And I don’t think you’re likely to find one that’s similar, or not at a reasonable price. I think there’s more chance of keeping your right-side bottom bracket cup in place.
In that past we’d have dabbed a few blobs of electric weld on the join between cup and shell. But nowadays I reach for red-coloured Loctite Stud ‘N Bearing Fit. Next I clean and degrease the threads (what’s left of them), apply plenty of the ruby nectar, screw in, wipe off the excess, and leave for half a day. Should you later wish to remove the cup, it’ll help to heat it to 250ºC, e.g. with a hot-air gun.
Red Loctite comes in small (£9-ish) bottles from good ironmongers and should do the trick. But if the threads are so far gone that the cup simply pushes in and out (rather than screwing in but jumping the threads) it may help to ovalise that end of the bottom bracket slightly: either hammer with cup in place or gently squeeze in a vice.
Should the red stuff fail: there are stronger metal-filled epoxy products, such as Loctite 3472, capable of spanning small gaps that’ll secure something the size of a bottom bracket cup, without any thread. This stuff is more difficult to use and comes only in trade quantities. A general engineering repair workshop is a better bet than cycle shops for that.
This was first published in the December 2014 / January 2015 edition of CTC's Cycle magazine.