Its a real pain in the behind. I model 2 rail 0 scale , circa 1920 to 1940 , give or take a year. What's available, in automobiles (for this period ) are few and far between. The Diecast market has been dominated by European companies, and their ) scale is 1/43 ,although there are some at 1/50 and a line of toy cars out of Russia that are in between. The trick is setting up a scene to trick the eye in to not noticing the size deference. Pairing the correct size vehicle and figuring to the scene. Dont cram all the deferent scales together. I have 3 19 -teens houses that are 1/50th kits , I uses as company row houses, I have a late 1930's English sedan parked in the 1rst driveway Looks like an Olds from the back. A 1920's Model T PU on the second , and Infront of the 3rd a 28 Chevy coop , they are 1/43. 1,50 and 148, all in that order and work in the scene! As far as finding them , train shows , , the web, and @ Bay. They are few and far between