Good morning, here is my answer. Last I heard ProComp makes the 440 Source distributor, but that isn't the problem I have with it.
Four years ago I bought a 440 Source distributor to save a few bucks. Then I built a really high performance 500 stroker with a large cam that needed a bunch of initial timing and very little mechanical advance. Well the 440 Source distributor uses metal tangs that you must bend to limit the mechanical advance. By the time you bend the tangs far enough, it warps the plate the advance weights rest on and the weights lock up. The distributor will work fine for a stock type build with a very small cam that doesn't require a lot of initial timing, but for high performance with big cams get something else.
I built a 493 for a gentleman and he provided me with a 440 Source distributor for his engine. After I showed him how it was designed we installed the 440 Source distributor and made a dyno pull. We pulled the distributor and replaced it with a FireCore50 and made a pull. He then pulled out his wallet and said, "How much for the new distributor, the FireCore50?"