[manikus]

There are only two references that I've ssen available, but I don't know their content per se, as I believe the books are available as pdf or print on demand.
One, is called Monsters of Myth and is by the same writer and artist as OSRIC. As you might guess, it's a Monster Manual, but different creatures and those that are the same have a different spin on them. (I'm getting all of this from a couple of reviews.) The other book is called OSRIC Unearthed and functions the same way as Unearthed Arcana did for 1e, but it's not the same material.
There are some mods, some of which might be reference books...hard to tell. But, as far as I can tell, only the OSRIC download is free, thought I did see some character sheets, etc at Goblinoid Games...