It's probably because the majority of people who drink Gatorade are fat-fucks or people who don't actually require them so the 01 and 03 series are not very marketable to sell at grocery stores. [I drink it too, even when I'm just on the couch watching Reno 911! so don't be offended.] They would just end up on the clearance racks if they were sold at Kroger, Albertsons, etc. Check out GNC, if you really want them.
I just got a bike seat with memory foam for $17. It molds to my balls and fat ass and is comfortable as fuck. (Edit: It isn't that comfortable but last time the inside of my ass was sore and I slept for about three hours when I got home. It gets the job done. I probably need to ride it some more and break into it.)
Edit:
They are at Kroger on the Gatorade shelves.