I think the purchase of old, rare books and commissioning the rewriting
of the information into modern volumes would be a valuable, charitable
purpose. As would the development of traveling exhibits.
As a 501(c)6, group sales where a part of the proceeds went to members
who created the prints would be allowed, but that would not be permitted
if incorporated as 501(c)3. And I think most members might be
interested in sales <VBG>.
A traveling workshop series would be a possibility as a 501(c)3 but
there could be problems if the presenters were members and received any
compensation. I don't think there would be a problem with a 501(c)6
organization.
David