The IUB Library collects topographic maps from around the world, with special emphasis on maps covering the state of Indiana. You might find them in GIMMS, the ALF, or the Lily library, but all cataloged maps will note where they can be found in IUCat.
GIMMS receives current USGS maps through the Depository program and retains them over time, but most of these maps are in the ALF. For immediate access to USGS Topographic maps, see the National Map.