Anecdotally, I once found myself IN this pet shop. It was in the Caledonian Road, North London. I wandered in - I was passing and needed something or other - and realised it looked familiar. Then I saw the signed picture behind the counter. It was a still of John and Michael in that "very boutique".
The shop-owner explained that when they'd done the bit on TV, they'd HAD to do it in the studio - for the audience reaction. But since this was for the FILM ("And Now For Something Completely Different") there would be no live audience. And with the superior definition of a film, a set just wouldn't MAKE it. Real pet shops have CLUTTER. And so they'd gone and found one - HIS.
I don't know if the shop is still there - if it is, the guy has probably made more money letting people be photographed there (like on the crossing outside the Abbey Road studios) than he has selling Norwegian Blue parrots!
...You HAVE seen the Argument clinic sketch, right??