The part about correctly picking every winner since 1976 appears to be a fiction added to the story in the course of traveling around the internet.
The two people running the Mock Presidential Election at WIU have only done so there in 2007 and 2011 (and they did correctly select Obama both times). A WIU newspaper (pdf) from November 2007 discusses the mock election but does not mention anything about any prior ones by those professors, or any track record of previous accuracy.
Those two guys previously worked together in 1975 at a different university and apparently conducted a mock election then, which correctly selected Carter, although I can only find secondhand references to that one. I can find no reference at all to any mock elections between 1975 and 2007, and their own website only says that they have conducted them “off and on.”
ETA: Also, please note that their Sanders prediction was made in November of last year.