Kate Schnakenberg was at a fifth store trying to find a wedding gown. Ms. Schnakenberg, 30, an operations manager at the Securities Training Corporation who lives in South Slope, Brooklyn, had made an appointment at Ella & Oak, which caters to plus-size women. It was a company she discovered on Instagram, where she learned it was running its first 10-week pop-up store, on West 29th Street in Manhattan.

“The last dress I tried on I couldn’t zip the back and the arm holes weren’t large enough,” she said of her visit to a previous store. “I’m a 14, which is the national average size. The fact that I can’t try on a wedding dress or know how it will fit before I buy it because they don’t have my size is irrational.”

She found plenty of options at Ella & Oak. Until recently, the company’s focus had been on e-commerce with the occasional pop-up weekend taking place in Dallas, Atlanta, Chicago, and other cities. This month the founders, Samantha Brody and Christine Callahan, opened their showroom in New York. They expect to be in the shop until March 8.