You can also check out the Mendix Partner page. Each partner page has a button to contact that particular partner to inquire about their services.
You could also try directly messaging developers from their developer profiles. If you click on someones photo in the forum it will bring up their developer profile where you will see a "contact me" link under their certification icon.
If you want to hire a developer, a job post can be placed here: https://developers.mendix.com/jobs/