GW,
I have all 10 cars (more on that later) and they are great. If you are modeling the late 1940s (1948/1949), Lionel released a TMCC w/Odyssey Rock Island E6 AA set (6-14521) in 2001 with cab #s that actual pulled the GS those years, #628 and #630. They would look great with your scale cars My E6s are in storage, so this is the best pic I have:
As Norm, mentioned, the separate sale dome is hard to find by itself. You do see it occasionally in sets that are for sale. There is a 10th car, a factory error dome. The 9-car set has two domes. The factory error dome has the name of one car, and the number of the other car. So there are three domes available if you count it. Problem is, the real GS had no domes