Does anyone know where I can buy a twin RF modulator - i.e. two a/v
inputs, with RF pass-through and preferably wideband channel choice?

I want to use it for a pair of CCTV cameras which I want to be able to
view on various TV's around the house. I was originally thinking of
daisy-chaining a pair of modulators together, but my existing AV setup
is very extensive (Tivo, Sky Plus, VCR, distribution around the
house...) so I'm concerned about the signal loss. I've already had
problems with signal loss after introducing new RF equipment into the
loop.

TIA for any tips.