Partsguy is right only Oem handset and software are legal to use on any mhe machines, you could buy handsets for electric trucks from zappi or Curtis but be aware some trucks use bespoke software so they might not work. Also you will need training from the manufacturer to be able to safely use them

Only legal way is from the OEM dealer and that is only if they are willing to let you go through their training.
You would have to be a very large end user for this to happen.