Sears is good for large boxes, my local Sears outlet will let me come down in the morning 1st thing and pick out what I want. Places that sell large office copiers usually have great boxes as well. Foam 4x8 1/2 or 3/4 thick sheets are available from Home Depot or the like. Cut easy with a razor knife, and with tape you can make about any kind of foam support you need.
