Wineguard has done a lot of the Dish R&D for most of the major DSS players as well as OEMS many of the Dishes. You can get just about any size you want from them or a local distributor. I have been using the 24" (60 cm) for most of my installs
that have more than 2 receivers. They cost about $50 for the dish and arm assembly, just use your old LNB. Get the most signal strength you can to avoid problems and signal outages.

hope this helps