I have no experience with these, but Swedish Microwave sells PLL LNBs that will lock to an external 10 MHz reference.
See
http://www.smw.se/products/pll10ref.htm
These might provide down conversion to the same L-Band frequency from two dishes (for combining).
You might contact Swedish Microwave direct to see if they have other options. I am in Northern Greece and would very much like to receive the BBC FTA signals from Astra 2D.
Regards,
Gary