I think yours is exactly the right approach. The fact that the company says today it is not going to reissue the book doesn't mean it might not revisit the issue another day or decide to use the material in some other form. It or the authors still hold the copyright.
That's entirely your decision and I'll respect it, but the forum already contains scans of out of print books newer than 1923 (which is the newest date for copyright expiration), so what's being discussed has already happened. And I'm sure I've seen books that are newer than the 1970's here as well.
The problem I see is that more and more men's tailoring books are going out of print and into the legal gray area of orphaned books; they're still under copyright, no one wants to release them into the public domain and no one wants to print them, so there's no legal way to obtain these books (and few libraries have them since they're a quite specialized area of knowledge). So, this is going to be yet another book that will be forgotten by time.
Can anyone name any respected, in-print men's tailoring books in English besides Making Trousers for Men & Women
Unless someone can convince the publisher there's demand for AT LEAST several thousand books
I doubt they can be convinced to republish, even a couple of thousand orders might not be enough for a republish (that would be barely worth their time). I believe the reason they've stopped publishing it is because FIT no longer uses it as a textbook so there is no longer a steady demand for it and they probably aren't interested in a one time order of a few hundred or thousand books. The only way I can see them reprinting is if they can find a market with a constant and steady demand for the book above several hundred books a year.
The only 100% legal alternative I see would be writing an open textbook on tailoring (which many of us would love to see happen).
The forum should decide how it wants to support people that want to learn by self-tuition because of all the books listed only two appear to be in print currently (by looking at amazon.com) Making Trousers for Men & Women: A Multimedia Sewing Workshop, and Classic Tailoring Techniques: A Construction Guide for Women's Wear.