Help Finding CD Player Mounting Sleeve?

I have a 2000 Lumina & a Dual CD1765 CD Player however when I bought the CD Player it didn't come with a Mounting Sleeve and the factory radio was 2x the size of the aftermarket CD player so it does not fit the original hole. I have searched everywhere for somewhere just to buy a mounting sleeve separately but everywhere says I can only find one if I buy it with the radio... Thanks in advance..