In one of my other lives, once upon a time, I ran a large format ink-
jet department. Those are the sorts of printers that would do 'photo’
banners. Make sure they’re using solvent ink. Pigment just sits on
top of the fibers, it doesn’t bond in. The printers I ran were
Rolands, and the solvent variety were known as “Sol-Jets”. There were
specialist inkjets specifically designed for fabric printing. I never
used them, but my impression was that they were Sol-Jets with a few
extra doo-dads to make handling fabric easier. These are $US 20,000-
$35,000 printers, so the local Kinkos won’t have them, but a banner
shop might. They’re not that uncommon. Now that I look at your site,
and see you’re in the DC area, I guarantee somebody near you has one.
I might try calling the PR office at the Smithsonian or Renwick, and
see who they get to do their banners.
Be aware that your range of colors will be pretty drastically
compressed. (The dynamic range on fabric stinks) You’ll get your
photo, but it may not look as sharp and punchy as you’d like. Talk to
the graphics guys wherever you end up. They know how to get the best
results out of their machine.