i dont think you can get them as they are a factory thing, but im certain a bit of silicone and some plastic sheeting stuff would do the job 
Great when you learn the hard way aint it. Its not essential to have them as if glass as been replaced at any point its probable that they've removed/made a hole in the membrane to access mechanisms. its just something thats there from factory. Better to have but you can cope without..
errrrrr Han, if you mean the membranes behind the door cards then you do need them.
The first paragraph is correct, the second, not so.
I'd give it a couple of nights of rain in the winter and your door card, carpets and sound deadening underneath the carpets will be p1ss wet through. How do I know ? Easy, because my Rallye had an hole in one and it soaked the carpets, not good.
The fix is quite easy, but slightly time consuming as you just need to get some polythene sheeting and good old duck tape and make a new one. I used the old membrane as a template, but you don't have to.
Read this little link to get the full low down on leak proofing a mk2.
Leak prevention ? Click me. 
