Don't think you will find much. Most dual configs are for servers so those that you do find will have pcie x8 only. I'd buy the 2500k and the extra that you would spend on the MB put into water cooling and overclock the snot out of it. It's funny, years upon years ago, there was at least a limited selection of dual cpu boards.
Your best bet is a company called Supermicro. They make dual cpu boards.