Those specialized devices are usually made in partnership with some third party ODM that's big enough to get Qualcomm's attention. Same for things like warehouse barcode scanners that run Android.

Even if you could get attention of one, and get it to design and make a custom device that wouldn't break the bank? You are still likely to end up with that OEM owning the design and/or binding you with a small pile of NDAs.

Another option would be to find a supplier that can get you some "fell off the back of a truck" smartphone chipsets, and either design your own PCB and roll your own software, or use a "fell off the back of a truck" reference design, SDK and tooling too. You'd need to be a real hardcore motherfucker to do that though.