Do they make an aftermarket supercharger for a 94 grand prix dohc 3.4 engine?

No, there isn't a readily available, off-the-shelf aftermarket supercharger kit specifically designed for the 1994 Pontiac Grand Prix DOHC 3.4L engine. While some companies might offer supercharger components that *could* be adapted, it would be a significant custom fabrication project requiring expertise and considerable time and expense. There's no easy bolt-on solution.