Need Balancers

Hi 
House built in 1970's.  please see attached pictures for identification for possible replacement
Anderson said it was a Prime Window, whatever that means
 
Another question, would you know if there is replacement string if I cannot get a replacement balancer?
 

As you can see from my pictures, my balancer does not have a tab on the side away from the strings do I do not think it will fit.
Now for the second question, do you have replacement string for those balancers?  
 
Thank you.