The small base models are getting real scarce. This is complicated by the fact that the easiest way to get the choke to work is to match the type of choke on the carb (divorced vs conventional) to that of the manifold, so you end up looking for a pretty rare item. The best place would be to haunt the swap meets if there are any good ones around. I use to be able to find them on eBay once in a while, but that source has dried up and was relatively expensive. They are making Chinese versions now which pop up on eBay at decent prices. Unfortunately, all that I have looked at were large base versions. One place you might check is putting a "Wanted" ad on the H.A.M.B. A lot of the older hobbyists are starting to "thin the herd". While most people won't will list something like this for sale by itself, they will respond to a "Wanted" ad if they run across one. I scored a real nice aluminum Mercury (Canadian) manifold that way for a good price about 6 months ago.
As always with "Wanted" ads, beware of scammers.