The wheels are by Irregular Miniatures, but the rest is constructed from Miliput and various odd bits of tube an metal. I will make a mould from RTV rubber so I can cast a few in white metal. The piece will be cast (without wheels) in three pieces, possibly four if I finish and fit the wooden 'gun shield'. I'll buy the wheels from Irregular Miniatures.
The gun shield is almost finished, but I'm not sure if I'll add it as I rather like the model as it is here.