5x7 black-and-white film still is available, as are modern 5x7 film holders. There are a couple of easy "tricks" for modifying the film plane to ground-glass distance. The simplest is to flip the ground glass around so that the textured side faces outward. This moves the plane of focus about the same distance as the plate-to-film-thickness difference. Not perfect, but it works for and old Seneca Black Beauty I own. Another method is to buy a sheet of aluminum the same thickness as a glass plate, and the same dimensions as a plate holder. Cut a 5x7" hole in it, focus the camera with the sheet in place, and then remove it to insert the film holder.
If you want to shoot 4x5" film, it may be simplest to convert a modern 4x5 back to fit the 5x7 camera. There are a lot of beat-up old graflexes and crown graphics out there for donor backs. A little help from a woodworker will put you in business.
Good luck, using old cameras is a lot of fun, and once you've learned their particular eccentricities, you can produce images as sharp as any new camera will make.