To give me an idea of whether the Annual Value (AV) of my property is fair, where can I find more information of the rental amount on private residential properties or HDB flats?

You can refer to rentals of private residential properties at URA website (Rentals for Private Residential Developments) and rentals of HDB flats at HDB website (Rentals for HDB Flats).
This information is sourced from IRAS
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