I personally use a matte spray brand called Plaid Patricia Nimocks and it comes in a blue black white label sold at Wal Mart in the craft aisle. It is a matte acrylic spray that doesnt make your models glossy looking. Others have suggested using testors dull-cote. I have never used it because i have always used the product i mentioned first and had no problems with it. Just spray it like a primer only spray it a little closer.
For primer i use Quick Color sold at Home Depot. Just be sure to pay attention to the cap and get the flat not glossy cap. It is only 97cents a can and is comprable to
GWs overpriced primer.