The updated soundtrack and the Digital Art Compendium are both now available for purchase on the official website, here.
The soundtrack, priced at 14.99 USD, includes the complete Skullgirls OST. The Digital Art Compendium, priced at 24.99 USD, includes character art, frames, environmental art, and other things. The Digital Art Compendium was originally only available to backers of the Indiegogo campaign, but it is now available to non-backers.
A second edition/disc 2 of the soundtrack is in the works for iTunes and Amazon so that those who bought the original soundtrack don't need to re-buy the entire OST.
It is also great to note that Lab Zero gets some of the profit when the soundtrack and Digital Art Compendium are bought, as well.