Some of this has been mentioned earlier in this thread, but let me summarize what I have discovered.
For 2D art, there are some companies that will fulfill orders on a print-on-demand basis. They buy various blank merchandise (apparel, mugs, smartphone cases, etc.), print the art onto it, process the order from the customer, package it, and ship it. In other words, they do all the fulfillment. All the artist has to do is set up their account and upload the artwork. These services are free, and the artist collects their copyright royalty when units are sold.
I would need to investigate how these companies handle multiple copyright owners, like group authorship, or derivative works like fan art.
The companies that I have come across so far that offer these types of services are CafePress, TeePublic, Redbubble, Teespring, SunFrog, and Zazzle.
For 3D printed art, Shapeways does print-on-demand and order fulfillment.