Your local bike shop will lace any wheel on a hub that you want. If all else fails, just build the assembly you need.
I would not convert a bike to disc brakes - there are no brackets for the calipers to mount to and in many cases the frame or fork are simply not designed for those kinds of stresses.
ebikes.ca in Canada will build you anything you want with their hubs - they have a mini-250watt geared hub that would be perfect for something not too go-fast.
LBS is an option for those willing to pay their prices (crazy high in Dallas, from my experience), but I am really a DIY kinda guy. I enjoy learning a new skill even if it takes a few tries and want to teach my kids to have the same tenacity.
Totally agree about the disc conversions, but I notice that my kids' Specialized bikes have caliper mounts already, but just have rim brakes mounted factory. I think at this point, it's all about finding the right used donor bikes and for that, we are on the hunt!