don't listen to pessimism.
here are a few. and folks like milspec monkey, he has resources for you too. that's how I started. am starting, i do prototypes for a lot of local guys, one offs, so for a guy like me, as long as you pay for the right materials, have your drawings and cash for the time, it's pretty straight forward.
https://www.wtfidea.com/oem-odm-contract/
https://overlandtailor.com/about-us
https://www.tacticaltailor.com/contact-us.aspx