Im not actually sure on the when.But the why might have more to do with technology and industrial scale of the war.The types of mobile forge varried from small gas powered barrel kilms to fire pits on a frames which looked more like a bbq.
Also alot of prefabrication ,more make it fit than made on the spot.
It was something That was looked at for the 1st Corps range,but its such a small area and has such a varried approach,that I couldn't honestly come up with a standardised kit.
As for offering.I've been having a little fun in my spare time writing tutorials on the forum.The first was for a Fokker Fvii plane in 28mm,and as asked I'm now writing one on Traction engines,and 8"howitzers as they require the same methods.
and could do the same for a mobile workshop.