You can find frames every now and then, a friend got a collection and I bought several frames form him. They seem to come along on the forums infrequently, but a bit more often on gunbroker. A frame by itself has to go to a FFL 01 (dealer).
AND, the number would never be the same plus to get period correct you'd need a mauser hump style frame, most do not have the hump (yrs prior to whatever year it is - see FAQ).
And keeping a frame as a spare - I have never broken a frame

But you could build another shooter, but then how is that different. An extra upper (slide) makes more sense, say, have one made in 7.65 or in a 9mm 6 inch barrel and swap it on when you want.
Ed