You may be able to pick up a board based on the Atheros AR9331, Alfa made one called the Hornet-UB [1], although I can only find them second hand (look for wifi pineapple mk4 for on ebay).
If you're looking to design your own hardware, there are plenty of ICs with dual NICs. For example the TI chip on the BeagleBone Black has dual ethernet NICs, but only one is used on the board.
If you're looking to design your own hardware, there are plenty of ICs with dual NICs. For example the TI chip on the BeagleBone Black has dual ethernet NICs, but only one is used on the board.
[1] http://www.alfa.com.tw/products_show.php?pc=99&ps=50