My aunt got turned away from consideration as a patient at Mayo Arizona a few months ago. They told me they couldn't take her on because they were overwhelmed with new patients.

Columbia Presbyterian takes Medicare, and they have an amazing surgical team. Johns Hopkins also takes it. And both of them are excellent institutions with the capacity to handle arterial involvement (although I don't know about mesenteric artery involvement specifically). Memorial Sloan also takes Medicare.
There will be other places as well. Those are just the three I can say with certainty accept medicare and are excellent.