Chris,
Trying to date this will be impossible without access to the MOD order books. While some regts began to changeover circa 2003 from a/a to silvered metal, some did not and there is no firm evidence that contracts were not still running to supply badges beyond that.
For NSN see this badge:
http://cgi.ebay.co.uk/WOW-LOOK-RAF-R...ayphotohosting
This maker does not specify anything other than BadgeHatRAF.
The last LI badges from Firmin were in a different packaging (sealed plastic bag) and did state 'finish:silvered' while their a/a Argylles were labelled 'finish:anodised'. I found a stock of these in a shop in Somerset recently both dated 2003.
Alan