Diamondback Outlook GX--Seatpost Diameter?

I have a Diamondback Outlook GX (not sure what year) purchased from an NYC
vendor who rebuilds and resells bikes purchased at NYPD auctions. After my
seat was stolen on the street a few months ago, I went to several bike
shops and none had a seatpost in stock that was the correct diameter for
the bike. In the end, a second-hand shop sold me a smaller seatpost and
manufactured a shim that lets it fit. It's a little awkward, but it gets
the job done. I'd like to replace it with a seatpost that really and truly
fits. Do any of you guys know what the exact diameter of the Outlook GX
seatpost is so that I can order one online?