Sorry - I don't know of a welder but I would think most motor garages would be able to weld them up.
Just ask if they have a MIG welder, this would be the most suitable way of welding up the chairs assuming they are made of fairly thin walled tube.
However the chrome plate would need to be removed with a grinder around the area of the joint as you can't weld through the chrome. Also the heat from the weld would probably discolour the chrome. You would then be left with a non chrome area around the weld and it would be even more bother and expense to get them re chromed!