If you like to follow Izannahs at auction, one way to do that is to sign up for lot alerts at auction companies which have sold Izannah Walker dolls in the past. Auction companies like Withington's, Morphy's, Bertoia, Theriault's, Frasher's, McMaster's and Skinner have sold Izannah Walker dolls. Occasionally they show up in other places such as estate auctions or Ebay. Some of these sites have the option of signing up for an account where you can name specific items that interest you. Then when that item comes up they email you.
There are also companies online like Liveauctioneers, Artfact and Prices4Antiques which facilitate internet bidding and/or track auction results. Prices4Antiques and Artfact have membership fees, to see realized prices. I try to track these as I'm aware of them here, but haven't compiled a list yet. You can find past auction results at these sites if you choose to become a member. It is really fun to see the variety of dolls that have come to market as well as the realized prices.