The firm, which rents out and sells formal menswear, sources its antique silk top hats from around the world and has around 1200 in stock.
Silk versions, which it sells for around £500, are rarer due to the demise of commercial production following the closure of a factory in Lyon in the 1960s that had produced the fabric.
Oliver Brown said there has been a recent rise in demand for these scarce silk hats, compared with the more recent grey felt design.
Antique examples for sale from the retailer include a c.1840 white gold beaver fur top hat.
The firm expects to hire out more than 1000 fur felt top hats, sell more than 500 from their own line of top hats, and sell 250 antique silk top hats around the Royal Ascot week of June 18-22.
The Oliver Brown brand name was bought by owner Kristian Ferner Robson in the late 1990s and operates from a shop on Lower Sloane Street in Chelsea.
It was awarded an official licensee to sell its items at Royal Ascot in 2017.