Several specialty publishers have reprinted "forgotten" books over the years, one of them Hyperion Press, back in the 70's, a few of which I have. You may recognize some of the names on this list, but most of them are obscure:
http://www.isfdb.org/cgi-bin/pubseries.cgi?199
I don't know if any featured time travel. And finding copies might be difficult, though I believe some are available as ebooks.
This guy was a little late:
http://www.isfdb.org/cgi-bin/pl.cgi?266251
But there may be earlier ones in there.
Gregg Press also had a reprint series:
http://www.isfdb.org/cgi-bin/pubseries.cgi?2335