Hubcentric spacers:
Mercedes 15mm Hub Centric Wheel Spacers Adapters 5x112:eBay Motors (item 110463662739 end time Dec-06-09 02:38:32 PST)

I get lug bolts here. Make sure you order ones with the correct seating (OEM is usually "Ball" / Aftermarket is usually "Cone" or "Tuner"). I'm not sure the length of the XF bolts. but my Benz ones are apx. 39mm. Just measure one and add 15mm to that.
Lug Bolts Mercedes BMW Audi VW Saab