The Westheimer Sales Co. was set up by Jack Westheimer and Bill Barnet in Chicago in 1958 to import Bongo Drums made in Japan. Westheimer is credited with introducing Japanese guitar makers to the idea of the truss rod, improving the quality and durability of the final product, and in 1959 importing Acoustic Guitars made by Terada and branded Kingston to the States. This added to his reputation as whilst not the first company to do this, they are credited with being the first major importer of Japanese Chordophones. 

By 1963 he had switched the manufacturer of Kingstons to Teisco and expanded the range to include Mandolins and Ukuleles; he had started importing Teisco electric Guitars, (branded Teisco), in 1960. In 1964 Westheimer started the new branding Teisco Del Ray.

Business took a number of twists in 1965, Barnet left, and a mail order company called King Korn brought Westheimer Sales Co. then installed Jack Westheimer as the President. While all this was going on WMI started importing Teisco Del Ray Guitars so Westheimer stopped using them and the branding went back to Kingston with Kawai now making them, (and in 1967 Kawai brought Teisco). By the end of the decade Westheimer Sales Co. was one of the biggest importers of Japanese guitars into the US but Jack could see Japan was getting expensive and so looked to South Korea, starting the trade there, and by 1975 Kingstons were being made there, (but I think Ukuleles had been dropped from the range by this time). In 1973, Jack brought back his company from King Korn and shortened the name to Westheimer Co. 

Kingston, (and Teisco Del Ray), wasn't the only branding Westheimer Sales Co. had, they also used Cortez and had something to do with Emperador on Guitars made by Hiyashi, (and later Matsumoko), though I've not seen either name used on Ukuleles. After the shift to Korea Jack partnered with the Park Family to start the Yoo Ah factory which evolved to become Cort Musical Instruments. The Cort brand is used mainly on Guitars but the range has included Banjos and a, (Dae Won manufactured), Banjolele. In 2019 three solid mahogany Ukuleles were added to the brand. This is also the firm that currently owns the brand name Stella, though I have yet to see what they use it for?