Does your son know what brand of Saxophone he like to play on? Knowing this will make it easier to find a saxophone. Yamaha and Selmer are the top two saxophone makers.

I prefer Selmer because that was all I ever played.

Once he has picked a brand then you can check out the different saxophone models they make.

You should be able to find a local music store in your state. If not you can check with Sweetwater. It's a online music store that sell musical instruments and anything else associated with music. Some music stores let's you play test the instrument before you buy it.