Is there Octopus Card is have a 3 days unlimited ride for the mtr and mtr buses in Hong Kong?

Strictly, the Airport Express Travel Pass would help. With this, you can have a ride on 1 or 2 journey(s) on the Airport Express (excluding travel between Airport and AsiaWorld-Expo stations) as well as any 3 consecutive days of unlimited travel on the MTR, Light Rail and MTR Bus (Northwest New Territories) (except additional travel on the Airport Express, East Rail Line First Class, and travel to/from Lo Wu or Lok Ma Chau stations).