An option is to create a UNION subquery. For this example, let's name it "qBook"...
SELECT VoucherNo, Suppcode, "AS" AS Type FROM tblBookings WHERE SuppFaxReq=-1 AND SuppFaxSent=0
UNION SELECT VoucherNo, Suppcode, "WHS" AS Type FROM tblBookingsWHS WHERE SuppFaxReq=-1 AND SuppFaxSent=0
UNION...