I don't know how to do what you want in a single step. You can do it in two steps by first creating a sheet with all of the individual PNG files. The montage command-line utility from the Imagemagick suite will do this.
A sample command that would apply to all PNG files in the current directory is:
After creating the montage sheet, you can print it with any graphics program.
montage *.png -geometry +2+2 output.png
You can find more information on the montage utility at: