Here in Europe there is Wephota films from Germany, they come in 25 and 100asa for 1/4 plate size. It is very good film.
Geert stocks it at
Dead Link Removed. Also Retrophotographic stocks it and also a German site
http://www.lumiere-shop.de/index.php?cat=c276_flat-film-Antik-Camera.html which has a large range of different sheet film sizes including 1/4 plate.
I shoot a lot of 1/4 plate size sheet film in my Graflex 3x4 super D, it is a nice size film, if I need colour, etc. I use a 6x9 or 6x6 Graflex roll film holder. They are super cameras Graflex slr's. I even cut down 4x5 sometimes, I've used TriX this way and soon to use Kodak Ektachrome. There are a lot of possibilities, but this is from a European perspective. Good luck, Anton