802.11ac I'm assuming. Why do you think USB 2.0 won't be fast enough? You can get around what... 50MB/s off USB 2? That's faster than anything you're going to get wirelessly.Adapting what to 802.11ac? An iMac? A PC? USB 2.0 wouldn't be fast enough. Maybe USB 3.0 would do it. Do you mean straight PCIe?
The other option is wired gigabit ethernet. In that case, the "adapter" Apple offers is the Airport Extreme.