It's from Alexandria Troas. The general type is listed a number of times here though not for Gordian III. Wroth's Catalogue of the Greek Coins of Troas, Aeolis, and Lesbos does list it, though: (This is available for free on Google books.) Here's an example for Caracalla: https://cngcoins.com/Coin.aspx?CoinID=146238 Must be pretty scarce!