I'm not (yet) a collodion photographer, but I thought this might interest the group:
I was at the yearly Bievres Photo Fair —just outside of Paris— on Sunday and I stumbled onto the stand of a certain Mr. Pep Mayugo, a woodworker and alternative-processes photographer from Barcelona (who speaks perfect English.. I photo'd his business card along with one of the attached photos of his products). He was offering some great looking hand-made sheet film holders, contact printing frames, plate drying racks, frames especially made for ambrotypes, small storage chest/boxes for plates ... But the most interesting (for me!) was his adapter backs, allowing you to use sheet film in plate cameras.
Disclaimer: I have no connection to Pep ... but I'll probably be a customer soon!