Just wondering if there's source code anywhere

Yes. The official site of the library is https://liballeg.org/, but this (allegro.cc) has been the defacto forums since 1999 ish. The licenses can be found here: https://liballeg.org/license.html. The source can be found here: https://liballeg.org/git.html. I'm not sure if that dates back pre-4.4 or not, but if not you shouldn't have trouble finding it if you search that site or the Web.

Append:

Download page for <=4.2 is apparently https://liballeg.org/old.html. You might still find that in the Git repo for all I know, but if not there it is.