Pretty much any sash lock that you can buy at the local hardware store will work on a Curtis Silentite window, and conversely the Curtis double hung lock would have worked on other brands of double hungs. Curtis went out of business long ago. See the attached picture for a Curtis lock vs. my recommendation of a good replacement lock to get.
My recommendation would be to get the Restoration lock made by Truth hardware if you want an old-time retro look. See attached or go to
For a bit more modern look and an excellent performer, I'd choose Truth's Entryguard II, go to