Curious Constructs had these pieces funded by Kickstarter some months ago. Now they’re available over in their webshop.
From the release:
At long last the 28mm Steampunk Inspired Artillery kits, which were funded by our incredibly successful Kickstarter campaign earlier this year have been released in store. Releases include the Field Artillery kit which includes a carriage and four alternate weapons, the Multiple Rocket Launcher, seperate Gun Carriages, a Crew kit, the Mule Logisitical Support Vehicle & Rocket Launcher. Check it out!