An interesting-looking collection (https://www.prestomusic.com/classical/products/9832204--malcolm-binns-a-90th-birthday-tribute) of 4 hours of music, issued early this month, doesn't restrict itself to unsung music but contains some works by Lyapunov, Alkan and Medtner. All reissues, as far as I know, and costs $30 at least, but might be worth a look especially if one wants his accounts of the better-known works as well (which do take up more than half the recording space, it's true).