I'm not sure about the specific saxophone stencils that were imported exclusively for the Dallas London music store, as there were likely many different models and brands that were sold there over the years. However, I can tell you that many music stores in the past have had their own branded instruments, which were often made by other manufacturers and then sold under the store's name. These instruments were known as "stencils" or "stencil saxophones."
It's possible that Dallas London had their own stencil saxophones made for them, or that they imported saxophones from other manufacturers and had them branded with the Dallas London name. Some popular stencil saxophone brands from the mid-20th century include Buescher, Conn, Martin, and King, among others.
If you have more specific information or questions about Dallas London's history with saxophones, I'd be happy to try and help you find more information.