I would like to buy for super cheap or even better free some small front turn signals and rear reverse lights. The front turn signals off an early Spitfire(see picture for reference) are kinda like what I am thinking. Obviously they don't need to be perfect but workable (aka not completely destroyed) would be great.
summit has a lot of misc lights if you're making something pretty much from scratch anyways. I was thinking about some round tails from there but I think I'm gonna keep my rectangle lights for now.
they have some round, 2.5-4" diameter lights in the auxiliary light section.
Just to put another option out there for you if you can't find something here
Street rod shops have a good selection of lights that may work. speedway motors is one I use.