I am always on the look out for a way to print and sell poster size maps economically. Currently the only remotely practical solution I know of is Cafepress and that is just barely economically. You will be paying a premium even if I don't add any profit. I can always just count it as a customer service focusing on the profitability with the main book. But the other issue is that is not bundled with the purchase of the original item (PDF or hard copy). You have to setup another account and pay a separate shipping & handling.
So I keeping an eye on what going on with Print on Demand. In doing this I stumbled onto the world of fine art printing. The basic gist is that you scan or upload a digital image and a print is made on canvas or fine paper that is near museum quality. It is printed and it looks like a painting due to the quality of the ink, the printing process, and the number of ink types (some up to 12 instead of the regular 3 or 4 ink process) .
Giclee (jhee-clay) is one of these fine art printing processes. Giclee Printing Services is one such site. A Lulu like site can be found at Imagekind. Now these prints can be expensive for example a Giclee 17" by 22" print (wilderland map size) is nearly $50. But if you want the best quality map possible this is the way to get it printed out. Some offer scanning services for additional $$$.
This is probably not a viable option for anything in OSR publishing but for the individual gamer it may be a great way of preserving or displaying their own maps at the highest level of quality.