This is largely due to the relatively low production numbers of the Impala SS and the associated lower demand for aftermarket parts. Developing a kit requires significant engineering and testing, which isn't economically feasible for a niche vehicle.
To add forced induction to a 2008 Impala SS would require a significant custom fabrication effort, involving sourcing components from other LS-based vehicles and potentially significant modification to the engine bay, exhaust system, and engine management system. This would be a very involved and expensive project.
