Here's a link for the heatsink: HP 507247 001 Server Heatsink for Proliant DL180 G6 490448 001 | eBayAlso - yes - HP 507247-001 is the right heatsink. Note that it does not have its own fan. The DL180 G6 uses a server cooling design with a plastic air baffle to force airflow over the heatsinks. Baffle is HP 507256-001 and should work any any 2U case with a midplane fan design (SM, Norco, etc).
I think you'll have to pick up the HP coolers to make it work because the mounting is so proprietary and you want a good seating of the cooler. You could probably get away without the baffle if you ghetto mod fans onto the coolers. But no matter what you do you are probably paying more for CPU cooling than you did for the MB - which is amusing!
Now... kinda funny that two cost more than the mobo.