There are a total of six different kinds of clothing stores in San Andreas. Three are unlocked when you finish the "Nines & AK's" mission, which are Binco, Sub Urban, and Prolaps. The other three clothing stores are Zip, Victim, and Didier Sachs. Zip is unlocked after first arriving in San Fierro, Victim is unlocked after you first enter Las Venturas, and Didier Sachs is unlocked after finishing the "A Home in the Hills" mission. Four percent of your total respect consists of clothing and so does 50% of your total sex appeal.
All of the clothes you buy are permanently unlocked, and can be accessed again in the various safehouses you unlock during the game. This allows you to mix and match clothing, meaning you can get the most amount of respect and sex appeal possible.