E39 525I TOURING MSPORT - WHERE TO FIND REAR SHOCKS?

Hello guys, been a while since i've posted. i'm having to replace the rear shocks on the touring rather soon but cant seem to find them anywhere besides the dealers. The thought of having to fork out around 5k+ per shock is leaving a rather bitter taste in the mouth. Does anyone perhaps know where else i could try for a set of these shocks? I've spoken to a company called GT shocks in Rondebosch. its run by a guy called Ian Glass. H builds shock for track applications but is also able to rebuilt shocks. Anybody made use of his services? Your input as always is always appreciated.

Thanks