3/8 shower rail and head, where to source

[Sharp Point]

As title guys n gals, just at the tail end of a huge heating upgrade and the custard has give me lots of extra's to do. In their ensuite they have a chrome rail coming out of the wall with a shower head coming out of it, the head is cream crackered and needs replacing......and Sod's law, it isn't 1/2" !!! It looks 3/8", so where does one look?


thanks