Depends upon the age and make of the saddle.
The old sterling that you used to be able to buy for them was from Diablo Silversmiths.
As for the newer saddles, I think they are being made (The silver that is.) by Montana Silversmiths.
Hope this helps! I know there’s nothing worse than losing just ONE concho! Grrrrrrrrr
The above poster’s right about Broken Horn, but duplicating another’s silver work is kind of a "no no" and I don’t think Mario would do that (Mario was doing my silver work LONG before he went to work for Broken Horn.).