You'd have to be very lucky to find a decent razor in an antique store. I did find an NOS Bartmann one time, but never a 7 day set. You will find that most vintage sets are 5/8. Two of my sets were bought on shaving forums' buy and sell.
I have 3 seven day sets. One is Wm. Elliot 21, 5/8. The days of the week are only on the case.
Another is Schulze, 6/8. The Schulze blades have some faded gold wash and the scales had abalone inserts that fell out. The Schulze straights came in a leather pouch and are supposedly from WWII Germany.
My last seven day set is Gondola Souvenir blades, around 7/8 with gold wash and other wash. I bought this one at the Mebane Antique Auction in Mebane, North Carolina. It was from the estate of a woman's grandfather and was also supposedly brought from WWII Germany where he was stationed. They definitely had not been honed or used.
All these are great shavers, but I don't use them enough. Vintage seven day sets can really save you money if you think about the price per razor.
Here is the Gondola Souvenir. Each blade is for a different city, except for one that just says, "Souvenir of Germany".
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Here is the Wm Elliot 21 and one of the blades:
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