(Moved to the For Developers section.)
I don't see any public information on the internals of the MR42, so I'm not sure how someone could develop an Open Source image. Are you saying that you're willing to provide them???
Can you provide a link to the device's hardware specifications?
Also, this link may be helpful to you: https://openwrt.org/toh/start
If a device isn't listed, it's not supported.