Blacksheep,
There may be military IRUs that do not bother with Mag Var but Honeywell Laserefs (all marks up to V in use on almost all Brand H-equipped aircraft like CL601,GX, Falcon 900 etc) and Northrup-Grumman LTN-101 Flagship IRUs (Airbus, CL604, CRJ) all have both Magnetic & True Heading outputs per ARINC 704.
The requirement is a bit more than tradition - VORs (remember using those?) and ILS still are centered on Magnetic Heading - hence my comment on our testing. It will be interesting if the FAA's essentially GPS-based future airspace comes to pass. There are already converter units that use GPS-derived parameters to generate True Heading from Magnetic and Lear Siegler proposed a cheap GPS-bounded inertial platform over a decade ago so how long will it be before a nearly pure GPS platform (or virtual platform) is built (but may be not certified)?