The snail mail took a while! I just received the USB-C to USB-A cable. I have plugged the rMB into my Satechi Travel Router which seems to be rated for 2A and the rMB is staying fully charged while I play a movie. So it looks like I now have several choices for cables and non-Apple chargers.The one I have on order is 1 metre. That company may have others. When I receive mine I will post here on whether it works with the rMB.
I will do some more tests with the rMB only partially charged.