Many of these "educational and cultural' historic groups or organizations are tax exempt and are required to report income and expenditures to the IRS.

I have seen annual IRS filings for a so-called "community" organization that has the same type of tax status and reporting requirements. But others dug those up, and I've never done it myself.

These IRS filings do not have to report donors, only the amounts donated, often with the names redacted. Which is always interesting when you see the checks for the multiple secret $100,000 and $200,000 checks anonymously given to some of these supposedly "grass roots* groups.

Some RR groups seem to have strong memberships, good donor bases, benefactors or "angels", and are well managed with transparent financials. I've seen reports available from groups I'm a member of over the years, but I never accessed them myself.

I believe that there are some sites that you could do a search on to tell you how to access or search for that information from the required IRS filings, or from applicable State finings for these non-profits, in the States they are chartered or operate in.