Dekka37,
Carlberkey has given you good advice about TheSwedishTiger. Might I also add that all you have to do is to conduct an
ebay search for what you want and then examine what's available in that particular vendor's store.
I applaud and am envious that you are purchasing US stamps from the 1940's and 1950's. They are beautiful and are among the most inexpensive stamps you can buy. They are my absolute favorites and my US MNH collection extends complete from 1920 to 2015. Of course, I don't have Scott #612!
Jack Kelley