If you don't have preexisting conditions, you can still buy PPOs from the big insurers as non-ACA plans.
Availability appears to vary widely, both from state to state and within states. If I lived in western Colorado instead of on the Front Range, I'd have a couple of PPO insurer options. If I still lived in Minnesota (where my previous health insurance policy was written), I'd have dozens of options from at least four different insurance companies.
I really miss my insurance policy from BCBS of MN.
Still, I was also one of those pre-existing conditions that simply could not buy any insurance before the ACA.