I have a bmw 1998 323is when looking for comparable cars I can only find the 323i?

For the E36 3-series, S means only that the car is a 2-door. The sport package was a stand alone option available on both 2-door (iS) and 4-door (i) cars.

FWIW, there was never an E36 323i sold in the US market. The 323 was only available as an iS 2-door. The 4-door 323i started in 1999, and was the later E46 body style.

If your car actually has the sport package, it added a firmer suspension, larger (16") wheels, and sports seats with larger side bolsters.

Suspension and a few extra tweaks to the powertrain and engine; a bit more HP. The 323is also only came as a 2-door 6-cylinder automatic. Some extra things like brake rotors are also different, so whenever you need to have any work done on the car or want to get parts you need to make sure that you emphasize the 'is' or you will have wrong parts in the car.

The 'S' does not stand for sport. However, it does mean that the BMW is a two-door model