NLB is an SPI game, so if a module exists, if won't be found on the vassalengine website.
See
http://www.vassalengine.org/wiki/SPI_Game_TitlesAs a quad game I'd scan each of the four maps to its own image file.
Add each image as a
Board under the
Main Map component in VASSAL.
In the
Main Map component properties, check "Can contain multiple maps"
After saving the module and loading it for play, you will be prompted to select the map.
For multi-map scenarios, you
add a row and
add a column to the layout, selecting a board for each quadrant.
As for scanning, check your local copy and office supply stores to see if they offer large format scanning. (I've seen it called engineering scan or blueprint scan.) My local Staples office supply store does large scans for $1.90 each -- I bring in my maps and a flash drive to save the images.
Since I don't intend to reprint these images to paper, 300 dpi is sufficient for my needs, saved as tiff or pdf. Rescale as desired in your graphics application -- save vmod images as jpg or png -- each board image has to be cropped precisely (with the same pixel dimensions) so it aligns correctly when displayed in the Main Map row and column layout.