I sympathize. Great cars, the old 6 series. Sadly hardly any in Pakistan ALTHOUGH I do remember seeing ONE in Islamabad, a 635, in a wonderful dark grey-silver colour sometime back in 2000/2001. God knows where it went or where it came from.
My lawyerly advice to you would be to try and sneak one in as a 'handicap-modified vehicle' under the provisions of the Import Policy Order 2009. "
Physically-challenged citizens are entitled to import any car of any age (yes, that's right, including a '57 300SL Roadster, a Porsche 356 Speedster, an Oval Window Bug...you name it)...so LONG as it's suitably handicap modified and you have evidence of how changes are helpful.
But you need to import as a handicapped citizen, or else it won't work.
Good luck.