If you want stock mounts, availability is hit and miss as someone cranks out a few. If you want poly, I have a new set I'm not going to use. You can have them for $100 plus shipping, which is less than I paid for them.
I got some for my 64 Valiant 225 recently. You can find individually or a set on ebay for ~$20/set. Do some checking since some listings are wrong and the photos are often generic. Autozone can get but $25 for the driver's side one and the same rubber type. My problem is they don't appear the correct thickness. The passenger side one is a bit too thin so the engine slants over too much. The prior owner put a worn disk brake pad as a washer to lift it up. Putting in a new mount didn't help. Maybe the driver's side ones are too thick, but the oil pan is already just above the K-frame. Search FABO, slantsixdan (god of slants) says the made in India rubber ones fail quick and better to spend ~$100 for a set of polyurethane ones. I'm a cheap bastard and will know in a year or so.
I have mounts on my race cars from these people. http://motormounts.net/
When inputing the vehicle, use 64 dodge Dart. Their online catalog is not correct for Valiant.