Your dealer was telling ya BS. They are available only through Canadian Nissan dealers. They won't show up as available in the USA. There are two part numbers you need: part number for the heater is 110016P700 p/n for the cord is 24076EC300. I called for a US friend that has and Xterra, I was quoted $59.94 for the heater and $60.01 for the cord. Hope that helps.
here's a write-up on the install:
here was a bit of a write- up about the install:
The location is on the passenger side of the block, in the front 1/4 of the engine. Typically the factory will install a frost plug of thin sheet metal designed to rupture in the event your coolant freezes to prevent the block from cracking. In our (Canadian spec truck) case this frost plug is removed and the block heater element inserted and has a 3 prong power cord snaked to the front of the vehicle with a male end to be attached to an extension cord.
The shop time to replace a block heater is 0.5 hours. To install a new one should be a simple matter of removing the frost plug and screwing the element in place (in North American built vehicles it is typically held in place with a wing nut on the back). However since mine came with one I can't be sure on the new install procedure.