Just use vector or a “AI Enlarger” tool to blow up the map pictures higher then 150DPI and print them on a board game format 20″ x 30″ four panel or bigger - with plastic cover and stick it to a concrete plywood piece of same size..
You can print these sizes at any online print company. Conquer Rome is awesome to play like this with friends at home (just use the real risk game objects on this map)
You can use "AI Image Enlarger", a online image enlarging tool which adopts AI algorithm to do the enlargement task. Make sure you get more then 150DPI minimum on your blow up picture otherwise it will look like crap (you will see the pixel dots)
Make sure you have CC approval if you do this (copy right) or tell your friends to sign up if they like the game
Its fun to build - you can make it as awesome as you like and if you play regular risk with friends, just take one of these maps with you like that and say "tonight we are going to play a different map"