I have been doing some research on various miniature manufactures who make 28mm miniatures, vehicles or terrain that would work in a Steampunk/Wild Wild West setting.
Here is a list that I have compiled thus far.
Brigade Games (Check out their Steampunk Line)
Clockwork Goblin Minis (Fantastic line of 15mms, but they will be coming out with 28s)
Elemental Miniatures (Achtung Cthulhu - More WWII Alternate Sci-Fi)
Empress Miniatures (Nice 1879 British line)
Ironclad Miniatures (Great looking Vehicles)
Knuckleduster Miniatures (Great looking lazer cut terrain)
Meridian Miniatures (Victorian Sci-Fi Figures)
Outlaw Miniatures (New Game with cool miniatures and vehicles)
Red Planet Miniatures (Looks promising for Martian lovers)
Spartan Games Dystopian Legions (Cool Figures and Vehicles)
Tobsen77 (Great looking vehicles)
Tsuba Miniatures (Great Line of Japanese Figures)
Victorian Miniatures (Galaxy's Finest)
West Wind Productions (Empire of the Dead looks real promising)