"Does anyone know if a Junker 52 or Ford Tri-Motor 1/48 scale can be found ?"
Have a look at aikensairplanes.com - they have a bunch of Tri - Motors at 1/43 at various prices, I think the cheapest is about $60, (weirdly, there's a humungus 1/38 scale one cheaper)all the way up to "nurse, fetch the crash cart!".
Hope this helps & good luck with the project.