In a quick search, I found the following...
-- A 1949 classified ad in a Dallas paper solicited a lingerie salesman: "Wanted to carry old-established quality line of panties, slips, gowns and negligees in nylon, rayon, cotton, crepes and satins in Oklahoma and Arkansas. Many established accounts. Straight commission basis. Non-conflicting lines permissible. Send references first letter; Gilbreath Mfg. Co.; Waco, Texas"
-- A 1952 store ad for lingerie noted that they sold "Quality styles--Carters--Faerie--Gilbreath."
-- Gilbreath's father was a cotton buyer in 1920 and the young Leo was working as a bookkeeper at a bank at that time.
-- In 1954 Leo A. Gilbreath (b. 1896/7-1983), Truett K. Smith, Barbara M. Smith, and Mrs. Olga(?) K. Maris were co-partners d/b/a Gilbreath Manufacturing Co. in Waco Texas.
-- A 1959 ad noted that Gilbreath Manufacturing Co. was at 320 Factory Drive in Waco and were "manufacturers of lovely lingerie."
--A very hard-to-read 1959 article about Gilbreath Manufacturing Co. noted that they more than doubled the size of their Waco plant and "Gilbreath Manufacturing Co. has moved to its spacious new plant in the West Waco Industrial District and now occupies ??,000 square feet. This is an increase of 3,000(?) square feet over quarters the firm formerly occupied. Gilbreath Manufacturing Co. increased its payroll by 15 percent after expanding and now has ?? employees. Truett K. Smith is president of the firm which manufactures lingerie."
-- A 1960 Dallas newspaper article noted that "Gilbreath Manufacturing Company, born in an old Waco feed store loft in 1946, is moving into a new $75,000 WID plant. Its owners expect to double its $400,000 lingerie sales to almost double that figure."