We're in the discussion stage of forming a photography co-op. First step, we announced our intentions to area camera clubs members (amateur & professional); and received about 20+ responses of which over 10 attended 1st meeting. We're now at stage of determining what form of co-op to create, a for-profit association or non-profit co-op ( we may do both with the for-profit handling various business ventures). Both types need registration with the State.
Your studio co-op would probably appeal to both professional photographers who need an adjunct to their on-site work, and amateurs who are getting into portrait or figure study. There is possibly a local affiliate of the Professional Photographers of America . Since forming a co-op is a big step, you might just announce studio space/time for rent.