My saddle bag is a Rivendell "Baggins" brand, the model is the "Little Joe".
They are no longer made, but sometimes you can find a used one for sale on Ebay. They are now sought after bags, so they are not cheap. I bought mine used for about $75- they might be more now, depending on the condition they are in.
Set up an Ebay search for: "Baggins" +"Little Joe"
and then make it one of your "favorite" searchs and set it to notify you via email when one comes up on Ebay.

Right now there is a Baggins "Hoss" model (bigger than the Little Joe) on Ebay:
http://cgi.ebay.com/ws/eBayISAPI.dll...ADME:B:SS:US:1
But really the Hoss is awfully big- not good for a daily bag like the Little Joe is.
For a bigger bag I use a Carradice "Nelson" in olive green:
http://peterwhitecycles.com/carradice.asp

The Carradice "Barley" bag pictured on the above link might be similar in size to my Little Joe.