No, as I understand it, unless you have an already approved plan or system (VA, Medicare, Medicaid) you must enroll through the ACA exchanges. Anyone here know more?
You can buy direct from the exchange providers for your state. Supposedly you can go to healthsherpa.org to see what the plans are and what they cost.
The current disadvantage of direct purchase is that if you’re eligible for a subsidy, they can’t give it to you. But don’t worry, Obama is working on fixing that (he says sardonically).