Challenge Checkers must be requested for any new cache as part of the publishing process. A reviewer will very likely not publish a cache unless it has a checker.
As pinkunicorn has directed you to, you need to create a new topic in this thread: https://project-gc.com/forum/list?8
Make sure you put your GC code, and the requirements for the challenge.
Please note that the challenge checker creators will not make challenges that are not within guideline (for new caches). The guidelines are listed here: https://www.geocaching.com/help/index.php?pg=kb.chapter&id=127&pgid=206