Has your son done events and showcases that would have gotten him in front of D1 schools? If he has, and he hasn't gotten offers by now, that probably means it's not the right level for him. If he has not, well, even in normal times it's really late in the game and unlikely that he'd get much interest unless he picked up a bunch of MPH's really quickly.
A LHP who can throw mid 80's over the plate definitely will get interest from high academic D3 schools. But even then, it's late. He would need to get to Headfirst in August and impress some people.
Funny thing about D3 is if you are right and he was able to get up into the 90's there is a path to the pros. It doesn't happen frequently but it does happen, especially for pitchers. Just this year, a kid out of Chapman, Nick Garcia, was drafted in the 3rd round. Funny thing is he started as a position player at Chapman and they turned him into a pitcher when they found out that he couldn't hit a curveball. The year before, Hugh Smith was drafted out of Whitworth in the 6th round. He had no D1 interest coming out of HS, but grew a foot and upped his velo by 12mph college.