Hi Steve,
You could try Brico [I think that's how you spell it]
It's got a big yellow sign and a bit like a B&Q [but not quite!]
It's on the main coast road on the right after Estepona, but before Benahavis. Unfortunately it's difficult to spot until you are driving past it so you may have to double back.
They have lots of plumbing stuff so I'm sure you'll be successful there.
Tom.