How do you unlock recon armor in halo 3?

Get all 7 vidmaster achiements [4 for halo 3 3 for ODST] then connect your gamertag to buingie and presto.

vidmaster achievements all of them, recon skulls or great map (put in fileshare if good will go into bungie fav's)

To unlock armor on halo 3 you need to get the skulls in campaign mode. You can get visual skull locations on youtube.

you have to get all vidmaster achievements to get recon.

There is no such thing as "Halo Recon" There is Recon armor, but "in Halo Recon"? Doesn't exist.