Got mine while fighting in a party with my brother. Dropped in a Brown Chest. Somewhat rare I believe. Haven't seen any drop while in party or other instances so far. Very Helpful in Dunes due to fire weather on a somewhat regular basis.
Finally got this a few days ago. pop it on during solo/party in desert and tada STR +5 (bringing my total to 27). Nice little piece of equipment if you're in a zone with Fire Weather... + good piece of equip for DDs leveling in dunes.