If you’re in Los Angeles or another major market there are various ways to access casting notices (called breakdowns). There’s a wonderful service run by the same people who post notices for agents/managers eyes only called Actors Access. This is where the best notices are posted. It’s mostly full of low/no paying work but occasionally a TV show will need something very specific and open the notice up to the general acting population. My yearly subscription to Actors Access is some of the best money I spend on my career. There are only two other legit sites in Los Angeles (LA Casting and Now Casting) but their pickings are slim by comparison.