How to pitch a jukebox musical, and who to?

Well working with a songwriter or composer will give you alot more freedom and flexibility, rather than trying to shoehorn in songs that fit.

If you're looking to use existing songs, that can get expensive quickly as it all comes down to rights; who owns the rights to the composition, the lyrics, who needs credit, when and where the song can be performed, in what way. It's a potential legal minefield, that you might want to avoid starting out. Where in the world are you too? Cause that can have implications.

Are you trying to pitch it to producers in the hope they can link you up with the right people, or to song writers to find the songs?
Most producers will probably be more interested in the final product ("Hey National Art Gallery, here's a painting I've done, would you like to hang it up? I've only drawn the outline" wont grab many). Have a look a different funds setup for development, try social media groups to see if there's likeminded people out there that you want to work with.

Have a look at:
musicaltheatrenetwork.com/
www.mercurymusicals.com
andrewlloydwebberfoundation.com/content/category/grants