I have a NOS Midland Ross brake booster but the silencer foam is falling apart under the boot. I was thinking of using some prefilter foam from a fish tank if I can find the right size. Does any vendors make or sell the foam. The mopar part numbers were 3699441 and 3699491 but none are around.

You could try Detroit Muscle Technologies. They make a lot of gaskets and seals for our Mopars.
Ron

https://www.detroitmuscletechnologies.com/

DMT , I looked and I didn`t see anything. unless I missed it. I don`t have a decent sample either.

Call or email him, as he may be able to recommend a foam for replacement.
Ron

Yes, you missed it. But its in a kit - not sure if its sold separately.

And the kit is........

B-body firewall gasket set. Might have to go on the site and look !!!

https://www.thefoamfactory.com/

This place makes everything. I just bought a roll of stuff to use as a gas tank trunk pad. If you can't find anything they'll have something you can cut to size.

Yup, went, looked, searched for "B-body firewall gasket set"

And the response was......

1752 results for 'B-body firewall gasket set'

Some day when I have hours of my life to waste I may pursue this......

Thanks for the suggestions. I think I may not have been clear in what I was asking. for. The part I am looking for goes under the rubber boot and around the booster rod, It is where the air comes out of the booster when the pedal is depressed. I assumed that someone that has rebuilt a booster would know what I am talking about.

Similar to this?

Y'know, its funny but I typed the exact same thing in the search bar, hit "return", then scrolled down FOUR ITEMS and low and behold there it was.

I think you're just a lazy SOB that wants everything done for him !!!

This is what I think. I think someone finds a specific answer to a question but rather than post that specific answer, posts a vanilla response like "google it", or "check the website", or "it's on the internet", or some other totally useless response. But then expects others to re-invent the wheel and duplicate the search effort just to prove they are not "a lazy SOB". I think you are one sick puppy.

That is probably close. I don`t know for sure as the old one disintegrated to dust. I tried a fish tank pre filter foam that fit but the one in your pic looks like the foam is more dense and might work better.

Looks similar to pipe insulation.