Ball and socket mirrors common across British cars?

I feel like I heard a hint somewhere that like many British bits 'n bobs, these are often fairly generic and shared across a number of different cars.

I've got a '73 MGB GT, and while I have the original rear view mirror base in place, its socket is void and empty of its original arm and mirror. I'm wondering whether I could be forunate enough that the base is the GT-specific bit, and that some not-out-of-production mirror could be obtained for the bits I don't have.

Anybody have any idea?

My experience is with Triumphs and Healeys, but I am used to decent reproductions being available, in a couple of styles (door and fender styles). Mirror heads are typically interchangeable. 

In reply to Ransom :

I'm sorry I can't answer your question specifically, but I can provide some (very blurry) images from the two MGB GTs I cannibalized.  The first is the best image and is of a chrome bumper '74:

The second is from a thoughly rusted '72.  The image is worse due to having to blow it up from an original photo print:

I'm guessing that if you can't find the mirror in the usual assortment of MG catalogs, you can still find one used.

In reply to keithedwards :

That's where I'm stymied; I'm after the interior mirror, and hte GT '70-76 is different to the scores of MGB mirrors out there. It looks like I may have sourced a used assembly, which will at least let me see what's behind me...

And further, a reminder of the perils of working from a partial assembly... Finally got a pic of a complete one, and the "socket" at the base doesn't appear to be used as such; not sure how it's assembled but the finished assembly doesn't look like it's meant to pivot there. All the more reason I'm feeling good about the used one I hope to acquire (I posted after walking away for a bit, but full marks to HundredDollarCar for calling the used route, and thanks for the pics  )

Just in case this thread someday is found by someone trying to sort a rear view mirror for a 1970-76 MGB GT, a couple of pics:

The base attached to my car:

What I gather a complete one looks like:

So apparently it's made from more than one part, but the notion that it was an adjusting socket was a bad guess on my part.

That socket is built that way to break off easily if you hit it with your head in a crash. Or while working in the interior. Snaps right back together, BTDT