morrissey wrote a letter to australian retailer the just group .
they own just jeans , dotti , portmans , jay jays , and peter alexander .
the group have so far refused to stop selling controversial angora wool .
singer to ask audience at sydney concert to sign petition against company .
morrissey has also banned the sale of meat products at opera house .
myer , david jones , sportsgirl among those who 've agreed to angora ban .