I want to make a lightweight 4 stage telescopic pole that collapses down
to about 400mm and extends to about 1000mm and would prefer to use
over-centre locks or the type that expand inside (as used in walking
poles) rather than a screw lock ... but I can't find any suppliers. The
tube can be square, oval or round and will need to be about 25mm max (OD
or width), but will depend on the available fittings.
So far the only suitable tubing I can find is round aluminium, but I'd
prefer to use oval plastic.

Any suggestions for suppliers of fittings or tubing?

Dave