Atwater was the company that produced the dies in the late 1940s for the F units that became part of the All Nation Line. They were well ahead of their time and many O Scale modelers still run them on their model railroads. I have a few of my own. The early castings have a small "Atwater" builders plate cast into their nose. I would think that the All Nation Hobby Shop would have sold the "Atwater" castings until they ran out of them.
As far as Varney/General Models/All Nation/Babbitt steam loco kits go, there was a 4-4-0, 4-4-2, 4-6-0 (original Varney B&O Ten Wheeler from 1946/47), 2-6-0 (Babbitt era), 2-6-2 (Carey Boiler) 4-6-0 ( Carey Boiler), 4-6-2, 4-8-2 and a 2-6-6-4 that was offered during the Genereal Models period in the late 1940s early 1950s for a short time. All of these models utilized the 70" Varney drivers and other parts. Frames are all bar stock (usually steel) with spacer rivets and bronze bearings from the original Varney design. The Mountain and the articulated have cast brass cylinders (probably Adams and Son) and the rest use the Varney Ten Wheeler cylinders, rods and valve gear. Properly assembled they will outlive their builders and can be made into very smooth running locos.
BTS (Bill Wade) in West Virginia purchased the steam loco line from Babbitt a few years ago but, up to now, has not offered anything from their inventory for sale.
These models in various finished forms and kits show up for sale with some frequency on ebay and usually sell for less than Babbitt was asking for their kits. That was probably a problem for the owner of Babbitt and may be why BTS has been slow in offering these kits again.
I think there is a decent market for parts to keep these locos running but I am not sure about the need for new complete kits. There aren't many people still building locos from kits or scratch anymore. I would guess there are less than 100 folks in our hobby that are doing this today.
Information above is based on my knowledge of the All Nation Line from personal experience with their locos and reading Model Railroader mags from the late 1940s and 1950s. Estimate of the quantity of loco builders today is strictly a guess on my part based on conversations with modelers at various O Scale meets around the country.
I will be finishing up my second All Nation 4-4-0 kit this summer.
Best to all,
Joe Foehrkolb