TFRRS has deep lists of 400m runners last year, 271 sub 48, 117 sub 47, 30 sub 46, and 4 sub 45.
Some examples of top teams with sub 48 runners:
Houston 6
Texas A&M 6
Baylor 5 sub 48, 3 at 46.00 or below!
Florida 4
Florida State 4
LSU 4
Texas Tech 3
Most NCAA track teams don't have a lot of sub 48 guys, although other guys on the team might be capable of it, e.g. 100/200/110mHH and 400mH, lj, tj (like Christian Taylor), and 800m runners.