DMsGuild/D&D Classics just released the "Classic Dungeons & Dragons Game" rule set, the 1994 revision of the black box. The file is currently missing the map and two of the tokens, but they've already noted it the description and have requested an updated file (however long that takes). Hopefully they'll release the Black Box scans at some point, too. I'd played one Red Box session for my first time playing, then got my hands on a 2E Player's Handbook (original cover with the Gold TSR logo), tried to cobble together an understanding of the rules between that and the 1E books I managed to get through inter-library loan, then got the Black Box for Christmas that year, finally getting a real start playing D&D - to this day, I feel that the Black Box (and the revised Classic Dungeons & Dragons Game) offered an introductory experience to character creation and role-playing that hasn't been offered since, but that may still be a more effective approach, despite the more complex core system compared to the streamlined d20 system framework.