Good Evening, c. w.,
Drums originally intended for processing 8 x 10 color prints are readily available on the used market for next to nothing. They will handle, of course, four 4 x 5 sheets. That works out well because four sheets will fit neatly on an 8 x 10 contact sheet. Unicolor, Beseler, and Chromega are well-known brands. I strongly recommend the Chromega; it doesn't leak as the Unicolor drums are often reputed to do. Whatever the brand, be sure that the drum comes with any necessary ribs and spacers. I have used the same Chromega drum to process 4 x 5 film for over twenty-five years and never encountered the slightest problem, except once when I carelessly failed to fit the cap on properly--that can cause a mess!
Konical