Wall-mart Blue, Target red and white, McDonald's various or black.
Business is based on the fact that if you lose a job where they force you to wear a costume, that is one bit a clothing you never want to wear again or even see. You'll be happy to sell it cheap or give it away.
Purchase an old
Amazon fulfillment center or similar and focus just on buying and selling and rehabbing the industrial costumes minimum wage high turnover employees are forced to buy or at least wear. Repairs, redyes, and alterations offered.
Mailing list offering to buy/sell would go to management of every fast food and department store in existence.
Provide cheapest freight prepaid envelope for any clothing persons wish to send after being fired. They will know where to get the new smock when hired again at the next hellhole.
Auction what doesn't sell quick enough. Or when one of the chains switches colors or goes belly up.
Supply costumes for movies, thieves, and start a whole new kind of cosplay event.
And in last resort bale and ship to Africa. (As in the book "Travels of a T-shirt" )