On some small D3's, if you can pitch 80+ mph and look like you know what you are doing on the mound then you're in...especially if you're a LHP. Catching poor programs might also pick up a guy.
There is a local, HA D3(top 10 academically nationwide) with a perennial talent deficit. If you are a slightly above average HS player, then you can make the team most years as a walk on. Trouble is, it's the sort of school where a 36 ACT and 4.0 GPA doesn't guarantee admission.