If you first insert a group on {@fiscalyear}:
{table.date}+184
You can then use a formula like this for weeknumber:
if month({table.date}) >= 7 then
datepart("ww",{table.date},crSunday)-26 else
datepart("ww",{table.date},crSunday)+26
At least this should get you close to what you're looking for.
-LB