Haymitch and Cinna were already spending time together, looking for ways to undermine the Capitol

That's a really interesting idea. I recently re-read the books too, and was struck by how involved Cinna must have been with the rebels in order to design (a) the wedding dress-turned-mockingjay and (b) the rebellion outfit for Katniss in District 13. I would love to read more about Cinna's history with the rebellion should you ever write it.

(Also, hi. I added you recently because I came across your posts on my friends-of-friends page and found them interesting :) )