Does anyone or any company offer a service manual for electric bike specifically for Rad bike or even better for RadRunner Plus? Something like maybe a good qualified repair man or company might have.
Honestly the information included in the product manual is sufficient for just about anyone with a good set of tools. Unless you mean electronic components?
Rad's knowledge base is a great resource as well: https://radpowerbikes.zendesk.com/hc/en-us/sections/360005403554-RadRunner
I don't think one exists that would cover electrical. Rad just swaps out electrical components; they don't repair controllers or displays.