Thanks! I am too, actually.
So, for those who are also working on some Jam hacks, here's my approach.
Head over to https://www.basketball-reference.com/
. The portraits there are 48x72 .jpgs, so you just need to move the portraits up a few pixels, resize to 48x56, save to .bmp and then work your own edits as needed (color transparency, convert to 32 colors, etc.).
Otherwise, for draft picks and some other players, I just grab candids off Google's images tab and resize/edit accordingly. I'm a fan of candids, so I make sure to have a few plastered in the game for fun. I always look for those where one of the shoulders trails off, so I can more easily fit it within the confines of the 48 pixel width, without having to show two shoulders oddly cut off. One is fine, since I can adjust it to the border of the team select box. Two just look bad.
Hopefully, this helps save some folks some time and gets their hack goin'!