Any decent parts house should have the oem engine mount, if you mean the rubber part. If you mean the the metal part that bolts to the cross member, there is a fellow on this forum named 4-5-6 trucks or something close who sells used oem parts who can probably help you. If your truck didn't come with a 292, you have two choices that I am aware of, replace the front engine cross member with one from a 292 engined truck, or contact one of the aftermarket vendors like Chassis Engineering and tell them exactly what you need. They probably have what you need. I'm sure there are other options out there. This is just an outline to get you started. Of course you can always build the mount yourself.
best wishes,
Les