You may very well do better by looking around.
Is this the item you are after?
http://www.stairlift-spares.co.uk/proddetail.asp?prod=0941
It would appear to be little more than a piece of 6mm, 1/4 inch or possibly 8mm rod with a couple of flats machined (or filed) at one end and a handle fitted to the other. (or possibly the other end bent to form a crank handle). I doubt it would be tricky to make one, given time and a few basic hand tools.
Note: If you want to try making one, it may be worth checking with a torch, to see what the receptacle inside the stairlift is like, just in case the supplier has used a generic photo.
XXX
August 2016