Hey There - for that many harps the Hohner case is a good bet. I used to roam with one of those and maybe a soft Lee Oskar 8-holder case (you could also go with two of those?)
You can find amazing custom harp case makers on Facebook.
I love my Seydel case! If you’re looking to acquire another 15 harps over the next few years, it could be a good option for you!
You can wee what I’m talking about in my Harmonica Case forum post.
Rock on,
Luke