Advice tips for getting ticket for Spanish Grand Prix as someone coming from Australia

Hey there, hoping f1 reddit community can help. I'm planning to fly into Spain a week before the Grand Prix, have accomodation booked -but am after a 1 day ticket to either Saturday or Sunday's Spanish Grand Prix on 22 or 23rd June. I wanted to know, does anyone know the best websites to safely buy tickets off? I'm happy to just get a ground pass. All the official sites i was trying to buy off for months would only offer 3-day tickets - and i can only afford (and am only there) in person to attend 1 or 2 days max. Also - any advice on tips on where to buy tickets in CBD itself, and how to get to/from the CBD to the track would be greatly appreciated. Thanks!