Try google flights. Use IAH for the outbound city, leave the return city blank, put in a date - the same one for both the outbound and return, hit search. You should also be able to narrow down by airline.
Or matrix.itasoftware.com , where you can search for an entire month at a time. You do have to put destinations, but you can try like 25 at a time. In the Advanced Controls, put ua+ (at least one ua segment) or ua ua+ (at least 2, etc.) in the routing codes boxes, then f !bc=n in the extension code boxes (to avoid basic economy, which won't earn PQSes). Select a calendar, a date, and 0 nights.