Oh after seeing all these great scratch built examples of steam vessels how can you not be tempted to try to build one...
Not tempted at all, I'm afraid. Eric the Shed's is rather nice, but it isn't exactly what most people have in mind when talking about a steamer for colonial gaming. It looks a bit too big and ocean-going to be sent on an expedition up the Congo or the Zambezi.
And while the simple home-made design is something of a classic among colonial gamers, to my eye they look a tad too blocky, toy-like and unrealistic. Sorry, not trying to belittle anyone's time and effort, but they aren't my cup of tea. I'm certainly not saying I could do better, just that I personally would rather pay money to have something nicer like those Sarissa ones posted above. I haven't seen anything on this page yet that would make me choose home-made over shop-bought.
And while it is nice that you are all posting your work here, the original poster was asking for manufacturers that make them. We are slightly in danger of that request being forgotten and this turning into a "post your steamer here" thread. We should definitely have one of those though, just maybe not in his request thread.