In fairness, I just wanted to post a meme 
Griffindor mentioned on Discord that he forgot he had one and that he hasn’t used it since the end of his first term. (I mean, just as a note, he remembered it a month and a half ago.) Maybe you’d consider it an institution, maybe you wouldn’t, but it’s been described as having worked on projects and implementing solutions — taken at face value, those certainly sound like “significant discussions” as considered by the Sunshine Act.
Instead of wrestling with what should be considered a sufficiently established organization to be deemed an ‘institution,’ I honestly just don’t think it’s that cumbersome to list them. We do something similar in the Charter for separation of powers purposes, and I think it’s pretty fast:
(1) Offices of the Coalition are the Delegate, the Prime Minister, appointed Cabinet ministers, the Chair of the Assembly, the Chief Justice, and any of their appointed deputies.
(I’m not saying to use the same list, just saying listing out offices doesn’t take that long.) If you wanted to include things like the Delegate’s Advisory Council/Commission/Committee, you can list something like “the office of the Delegate” which I think can be understood with common sense as meaning — if the Delegate works alone, then obviously they don’t have any discussions needing disclosure, but if they appoint staffers/advisors that have significant private discussions about eventually public projects, then those are reasonably understood as being discussions within the Delegate’s office.