Every service I'm aware of that produces large format prints from film will initially scan your film into a digital file anyway. Cutting out the middle man will allow you to use a color-managed workflow and most likely produce better outcomes.
That being said, you can either go with a service that performs digital to film conversion for the film industry (film-out service), though these are rapidly vanishing. The biggest is called CineLab I believe, you'll want one that provides a 70mm or 120mm service if you want to preserve as much of resolution modern digital cameras can provide as possible.
As far as procuring your own equipment, for high resolution, you're looking at a laser based system (Kodak makes, or at least made, one called the Lightning II or Arri makes the Arrilaser) or a DLP film recorder. Any of these you're talking very big money.
You might also see if your preferred printer provides printing to a large-format transparency film as an intermediate.
Again, I advise against using this method as the lost in quality by taking digital with all its flaws, then projecting that onto film with all its flaws, then putting it through film scanning with all its flaws, and finally printing all those compounded flaws through your output medium with all it's flaws... you get the point.
If the desire to go through film is artistic. Shooting on film, then scanning and doing whatever graphic design is desired, will give you the "look and feel" of film that will carry over into the final product better than taking a digital image and putting it on film in the middle of the process.