The switches/LNBs are readily available from a bunch of places - including this site's sponsor.
Sounds like you have a pair of Legacy Dual LNBs ties to a pair of SW21's.
If you're NOT going to need a third bird, buy a DP Quad.
If a third bird is in your future, buy a DP Twin & DP34.
If you might end up with four birds, DP Twin, DPP44 ($$$). This setup saves you from having to run an extra RG-6 to the 921 if thaat's a concern (probably not for you

).