Supercharger kits.
 

where can i get a supercharger kit for my GS4?

i need web sites.

thanks.

RMM may have a few lerft, but they are not producing them any longer.
http://www.rodmillenstore.com/gs_400/price.htm

SRT used to, but they also are not producing them any longer.
ww.srt.com

If you are dead set on SC, you may need to go the pre-owned route.

Also, try a Search. SCs have been discussed many times over here.