Odds of Getting In
How have you not gotten orthognathic surgery yet? Everyone's doing it.
Okay, maybe not everyone. But still, oral surgery is relatively common. Just look at wisdom teeth. About ninety percent of people have at least one impacted wisdom tooth (source). And there's plenty of other, quite serious OMS problems to go around: oral cancers, tumors, cysts, and structural deformities. Whatever your specialty in OMS, you'll be able to find a group of people willing to pay for your services.
You can up your odds depending on where you establish your practice. Employment right now is highest in California, Texas, Florida, and New York (source).