The first is here is the states (http://www.jgairguns.biz/
>). John is good, but, has a limited supply of BSF parts.
The second is in Sweden. His name is Matts Hammer and email is: email@example.com. Or you can check his website www.hammerarms.com. I've dealt with Matts on a number of times (I have a Wischo 55D) and he is trustworthy. It's a bit of an odd transaction as you mail a MO to his uncle in Minnesota who relays payment to Matts. Matts ships from overseas and it does take a week or two.
I would contact both to see if they have your parts. Matts would be the person if it's going to be a hard to find part. Don't be put off by the logistics of the transaction.
email me if you have more questions.
p.s. Matts actually offered my a nice BSF 54 two years ago that I passed up. Good price too.