I think it was 2004 that they started using the embossed aluminium headbadge rather than the decal. Contacting Rocky Mountain to get one is likely the best plan (although Jen Green does beautiful custom headbadge work).
From 2004 ETSX 70
from 2006 Slayer (with black mountain background)
They're likely to be a bit protective about things like this so that no one sticks a RMB headbadge on their Nashbar frame to boost the ebay sale value, so send Rocky your frame serial number in your request and maybe a picture of your headtube.