You can try calameodownloader, followed by your vehicle designation and see if that brings up anything.
Also may try google with the vehicle type then "varients" or specific type.
Sometimes really obscure or modified vehicles aren't well documented or photographed, finding info can be next to impossible, at a minimum very time consuming.
You may also try looking up German engineer or Pioneer vehicles, may get a hit from that. Good luck, happy modeling and Happy New Year.