Typically an archive will have a collection development policy that lays out the ground rules for acquisitions and processing of donations. I'd advise your group to speak with the archive directly to find out if they are interested in the materials and how they will process these materials. Digitization is a very labor intensive project and the content isn't always made available to the public, so you'll need to clarify its public accessibility with the archive. Typically, when someone donates a collection to an archive they are surrendering rights to the material and placing it in the hands of the archive. And, also typically many archives have a backlog of materials to catalog and in some cases digitize. So those are both points worth discussing both internally and with the archive.

It might be helpful to speak with the archive directly about whether the project could be digitized if your group helped find the funding. There aren't any groups that fund radical archive projects specifically, but the Foundation Center has a number of different funding organizations and grants that support media projects, labor projects, library projects, etc. You can access the Foundation Directory's online listings either at a public library (usually need to be on site to access) or if you're in NYC you can visit the Foundation Center at 79 5th Ave.

There are also Library Service and Technology Act Grants which provide money to library projects in a particular state once a year. The archive would need to apply for this directly.

Another option that some archives have done is to contact the people the materials are about and ask those people to donate towards the materials preservation.