I found the latest versions of the GnuBG benchmark databases here. They've moved around in the 10y since I last looked for them! The file format remains the same, though I had to rebuild the parser for the 20-character string board descriptor in here.
Remember: the benchmark databases given a bunch of starting boards, rolls, and for each, the top five boards with post-roll equity for each.
There's also a set of training databases that gives a list of boards with pre-roll probabilities for the different game outcomes; that's what we do supervised learning against. Those are here. A description of the contents is here.
These training databases have grown substantially in the intervening years: there are now 1,225,297 entries for contact, 600,895 for crashed; and 516,818 for race.