Well, I just used Google: "chaparral feedhorn 11-1329-1 "
They can be had for about 1/2 of list.
But another company, ADL, also makes a similar device.
(not to be confused with
dual-band Orthomode feeds for C & KU - they're an arm 'n a leg)
There are Chinese C-only models out there, currently in production.
Saw one in Stogie5150's latest rebuild pictures:
How I Learned To Love The Bomb...Or...Paraclipse Modifications......
If you do go that way, then it's probably also worth a more involved discussion of C-band LNBs, too.
But, most of the above has been discussed here on the forum, so it's a good resource for more info.
And someone else made a feed with two LNBs built into or onto it.
Don't think they were removable.
I forget the name or the brand (Pico Macom ?), but saw it in a picture LinuxMan once posted.
Think he found them surplus (or in-service on an old dish), and I don't know if they're currently in production.
(oops, found 'em listed on the Global-CM web site, so do some Googling for more info)