AB,
This is incoherent. If a "source" does not function deterministically then it's random; if it doesn't function randomly, then it's deterministic. Your way out of that is essentially "it's magic", which is epistemically worthless.
Just re-read the Wikipedia article on free will. Still don't understand most of it, but at any rate there is a position called compatiblism, which says that determinism and free-will can co-exist, and some compatiblists even say that determinism is
neceessary for free-will to exist (presumably because without it, everything would be random). I have read of a distinction between "strong" and "weak" free-will, the weak version being that all decisions are determined, but some of the determinants are the subject's conscious choices. It was determined from all eternity that I would light some 'Prince Albert' in my Blakemar Rhodesian pipe about ten minutes ago, but it was nevertheless my choice. Strong free-will maintains that I could have decided not to bother with a pipe, or chosen a different one, but that is probably incoherent. Or something. Probably just as well that I used my weak free-will to decide not to be a philosopher.