Let's list some relevant (lists of) authors and associations thereof, especially for architects and visual artists, whose alleged representatives are most vocal.
In UK pretty much all professionals' societies have spoken in favour of FOP, work done? They should be involved in contacting the others.
- Architects: 
- Photographers etc: The Times
Do they have any real association?
- EVA: not a real association, just collecting societies under another name, mostly working for the sake of the French one
- Federation of European Photographers
- UK: BIPP, supported FOP in The Times
- FR: GNPP
- Any Europe-wide association or way to contact? This is a huge population, hard to manage.
- IT: ANITEL contacted