Silverline window balances aren't made anymore! I know, right. Its exactly what you've been looking for but cant find the replacements to fix your Marvin windows. Luckily we have found a solution. Our series 350, block and tackle with the correct attachment will replace the Silverline window balance. This balance isnt listed online yet, but general block and tackle balances can be found here.
Ask us for more info, as we can help you get the best attachment for what you need. Silverline tilt windows have some specifics that need to be looked for and we are ready to help.