From what I understand of that system you could just find the number of days from the start of a given year and then calculate the week and quarter based on the number of days and length of each quarter. You might need to take into account 53 week years, but this should get you started:
New Table( "Fiscal Week",
Add Rows( 1000 ),
New Column( "Date", Numeric, "Continuous", Format( "yyyy-mm-ddThh:mm:ss", 19, 0 ),
Input Format( "yyyy-mm-ddThh:mm:ss", 0 ),
Formula( Date DMY( 4, 1, 2021 ) + Row() * In Hours( 12 ) )
),
New Column( "Fiscal Year", Numeric, "Continuous", Format( "Best", 12 ),
Formula(
Floor( (:Date - Date DMY( 4, 1, 2021 )) / In Days( 52 * 7 ) ) + 2021
)
),
New Column( "Fiscal Day of Year", Numeric, "Continuous", Format( "Best", 12 ),
Formula(
Floor( Mod( (:Date - Date DMY( 4, 1, 2021 )) / In Days( 1 ), 52 * 7 ) )
+ 1
),
Set Display Width( 67 )
),
New Column( "Fiscal Week of Year", Numeric, "Continuous", Format( "Best", 12 ),
Formula( Floor( (:Fiscal Day of Year - 1) / 7 ) + 1 ),
Set Display Width( 85 )
),
New Column( "Fiscal Quarter", Numeric, "Continuous", Format( "Best", 12 ),
Formula( Floor( (:Fiscal Week of Year - 1) / 13 ) + 1 ),
Set Display Width( 65 )
)
);