Hi skytrainboy
I've never seen a commercial kit of an aircraft factory - I think you're really talking dioramas here... :-)
Many years ago, Shep Paine modelled a B-26 Marauder production line in 1/48 scale! If I remember rightly, he built a single plane, surrounded by figures and equipment, and used mirrors either side to give the effect of a production line stretching into the distance. :-)
Hope this helps
Rowan