The usual way to get an XF turbo is to do a custom job yourself, getting 2nd hand and reco parts, like getting a truck intercooler fabricated to fit, finding a reco T04 or similar and getting manifolds and pipes made to suit. Ive seen one kit, but that goes for $5000 and doesnt include an intercooler. Im going about slowly converting an XE to run on straight gas with a T04. Try doing a search on www.performanceforums.com
, there is heaps of info there.