Since my answer to everyone is always the same, I thought I'd post this here as a helpful link for people who visit my blog.
I received my 1962 Breviarium SOP from a monastery of Dominican Sisters. I received my 1959 Dominican Hand Missal from a cloister of Dominican nuns. I think many, if not most, of these monasteries and convents have been cleaned out by now, but it is always worth a call or visit to see.
But the remainder of my collection, was obtained by vigilantly checking online used book venues, in particular ABE Books.
If you are vigilant, you can find the 1962 volumes on ABE Books or Amazon...but you have to keep looking. They go quickly. Also, it is highly unlikely that you'll be able to find both volumes at the same time. It took me nearly 2 years to obtain both volumes of the 1909 edition. One volume came from Germany and the other from France.
When you search ABE Books (which I believe is the best site), go to the "Advanced Search" tab and use Master General Michael Browne's last name as the author, and under Keywords use "ordinis". There were only a handful of liturgical books published under his Generalship, including the 1962 Breviarium SOP. The same goes for older editions. If you want to search for the 1909 Breviarium SOP, the author would be "Cormier" and the keyword would still be "ordinis". It's that simple.
Keep checking. Be vigilant. Don't get discouraged. Veritas!