Radwagon 4 Rear wheel replacement conversion to non e bike

[joe2003pc]

I came across a deal for a Radwagon 4 frame with accessories for a really good price.  I've been looking for a non electric cargo bike to haul my kids around town.  I'm a cyclist, I can make enough power on my own to get around.

Anyways, the bike doesn't come with the rear wheel, The motor was damaged.  I'm looking for where I can buy a wheel/hub that will fit and I can put my own cassette and shifters on (probably some version of Shimano MTB).

From what I gather, the dropout spacing is 175mm with a 12mm thru axle.  I haven't come a across this in a non ebike format.  Does anyone have any experience or suggestions on this.

I have found that the 22" wheel that came with it doesn't have a lot of tubes/tires available so I'm probably looking for a 20" wheel.