Oh my answer is too late! Hope you did find a charger!
A large shop called "Verkkokauppa.com" usually has Mavic Air Power Adapter (P1C50), Mavic Air Car Charger (C3S60) and Battery Charging Hub available. And propellers etc. parts too. "Verkkokauppa.com" even has a 24 h open kiosk in Helsinki. Use dotcom (or pistecom in Finnish) with that name, Finnish word verkkokauppa means just a "net shop" in English.
"Rajala Pro Shop" (rajalacamera.fi) very close to Helsinki main railway station is worth check too.