Where to find puzzle designers?

Jigsaw puzzles, crossword puzzles? Care to narrow the range?

this is for a digital application. Any puzzle design within that constraint

I suggest that you start by looking where puzzle creators sell their own material.

If there are still puzzle magazines out there somewhere, like the magazine that is or was edited by puzzle maven Will Shortz, they do/did buy original puzzles from freelance contributors. Find some, study them for applicability to your needs, and see if you can get in touch with the authors through the magazine.

In fact, any magazine that publishes puzzles (whether or not that’s the main purpose of the magazine) might offer the same possibilities.

I don’t know how you might contact them if they’re online only, but I’m guessing there’s a way.

Joseph Young is a brilliant blogger who creates and edits puzzles. He often contributes to Will Shortz.
Here is a link to his site Puzzleria .
That would be a great place to start.