Large format printing:
Kinkos, I'm pretty sure, has large format printing.
Some local photo stores have large format plotters, as do blueprint reproduction shops.
They tend to be pricey, like $6 to $10 a square foot, depending on the paper, ink, etc. Get either UV ink or Coating to preserve the color.
Then there are online sevices. For example, there's
Poster Print Shop but I've never used these services. Plenty more of these around.