Gars are biters IME but many keepers report favorable communing of gars with other fish. I'd try something simple, like Synodontis euptera, or Pimelodus blochii, or a raphael catfish... in the order of decreasing ability to tolerate their conspecifics. Raphs are fine with each other.
None can be too little or they will become a prey. If your gar is 1', I'd say the cats need to be at least 6" or bigger.
Larger woodcats, like jaguar wood cat, or smaller Pseudopimelodidae, like Batroglanis raninus, may work too.