First, super restoration project and love your restoring a piece of Americana. Understand you want original Sinclair, Washing, and Lubrication porcelain signs.
Consider having a local painter/artist paint on the building surface(s) scale sized painted signs. Then as you can acquire originals, hang them directly over each hand-painted place holder. Find a local high school art department or local artist that needs some work during CV19 times.
This would provide a nice look/theme on the building while giving you time to acquire all the original porcelains.