Twin Breakers 15A single pole Bolt-on type for Sylvania Panel
Bolt in breakers are usually utilized in commercial and industrial panel boards. This could also mean you should not be messing with this panel at all. But assuming you are qualified to open this panel, remove a bolted in breaker and replace the breaker, you can easily find the correct breaker.
Look on the inside of the door. There will be a list of the correct breaker types required. Write it all down and like HIVOLT said, take it to a supply house that sells or reps this equipment. If unsure bring old breaker on shopping trip.
Home Depot nor Lowes nor any box store sells these types of breakers. So, don't waste your time with them.