As a local Gun mag here in New Zealand had a story about one of it writers using one while in the States when he was shooting praire dogs, But I can't find any trace 204 cal rifle on Browning's web site.
Two of my friends have had A-bolt Medallions in .204. As a previous poster indicated, it was a special run of Medallions made in .204. They have 22 inch sporter barrels.