We do not have the .OBJ files for the Original CE Mark V in the armory, however, I believe you should be able to export the .PDO files as .OBJ if you have the paid version of Pepakura Designer. It is possible that that the ArmorSmith program can also export .PDOs as .OBJ files.
Other than those two paid pieces of software there are several "Free" (Ad Heavy/Ad Supported) sites and programs that claim to be able to do it, but Pepakura and ArmorSmith are well vetted and trusted programs in the community and well worth the cost.