I recall seeing a huge list of guilds that might visit Trollskull Manor looking for work and payouts. But I don't remember where. Might have even been in these forums but I can't track it down. Anyone recall?
The old 3e sourcebook Waterdeep: City of Splendors lists all the guilds in the city. There might be something in Rise of Tiamat since the Council meets in Waterdeep. I think alas you will have to scour the Tavern chapter of Dragon Heist with a fine-toothed comb to compile a list, and it will still be partial.