External antenna on DIR 825

[pinnocchio]

I have a couple of DIR 825 routers I picked up cheap off Ebay.

I'd like to fit external panel antennas for a specific project, however I can't find any decent panel antennas that support dual channel and will give me around 18db gain in 2.4ghz for a reasonable price.

Any suggestions/recommendations?

Alternatively is there any way to split the output signal to two different antennas, I'll be happy to have the 5ghz on standard omni antenna with a 9db gain.

Thanks in advance.