I talked to the lady who gets my supplies and she says that the plastic will crack in freezers. The problem with metal is that it rusts. Maybe that's why "freezer lockers" don't exist. The CD cases are definately too small for my purpose.

Anyway, the best I've been able to find is this plastic lockbox but it's from the U.K. My source said she'd look into it, but she wasn't sure that it would withstand freezer temperatures. Click here for picture

My other option I found is a metal portable file holder with a lock (about 13 X 18 X 10 3/4). Only problem is that it's kind of expensive ($117 CDN) and if it's going to rust, it would seem like a waste of money.