Looking for bathroom tiles used in the 1960's to replace broken ones?

Thrift stores in your local area might be a place to start. If they are the Goodwill or Salvation Army type stores, Their turn over rate may be such that something that old will go out the back door quick. Try older "Junk or Salvage yards" in your area.

Inquire at local Mom & Pop hardware places or a trusted local tile guy that does rehabs and restorations. You may even find an " Ooo Ooo Arts Deco " shop that will have a source.. Keep in mind that old is IN and a Chinese guy may build you what you want, if you order enough.