These are embedded devices, which each need their own bespoke image exactly tailored to their (hardware- and software) requirements. There are no 'generic' images that will work on multiple different routers, either your exact model (down to its hardware revision) is supported - or it isn't (if it isn't, you may be able to propose a pull request adding support for it, but the necessary down-to-the-hardware development would be all yours, as you're the only one with the hardware on the desk).