You would get the the monthly allocations from the allocation slices.
But you will get to the problem that the available hours vary by the month
The slices are in PRJ_BLS_SLICES tables.
The slices for the user defined daily availability the request ID is 1 and for the monthly it is 7.
There are also system/insta slices in PRJ_BLB_SLICES_M_AVL and PRJ_BLB_SLICES_D_AVL
which have system defined sliced periods.