Thick outer vinyl sleeves

Are you talking about outer sleeves that cover the album jacket? Sleevecity.com has them (although I'm not sure they're as thick as you require):

http://www.sleevecityusa.com/record-sleeves-s/1828.htm

Sleevecity has 5 mil outer sleeves. Yes they can pretty well stand up on their own.
I have several thousand of them.
Only problem is they tend to be slightly different sizes when from different orders. So some will NOT fit over double albums. This is annoying, but I have enough which were bigger so I can swap them.
I do not know if they have 'fixed' this annoying issue with their sleeves or not. Last I ordered some two years ago.

I recently read on another forum that the size issue has been rectified.

thanks for the information. will follow your advice

just bough a package to verify if they are what Im looking for, thanks again.

Mylar record sleeves available at bagsunlimited.com as another option....

thanks, will considered also but they are expensive