The silents were exclusive they are recently available to the mass market, so they are starting to turn up in boards other than corsair finally. The first I saw was one from mechanicalkeyboards.com, their new board the Fission https://mechanicalkeyboards.com/shop/index.php?l=product_list&c=368 they have pretty much all the cherry switches and the silent red.
There is no brown varient yet as it is a modification the the stem to make them "silent", you can make a black by swaping in heavier springs but the brown slider does not currently not have a production line for silent variant, not sure if one is planned but I have heard some support for them for them community in an interest way.
Edit: there is a mod to make them yourself, some liquid latex on points of the slider will make you a silent variant of any cherry switch but takes effort, super time consuming, more an if you are already taking the switches out may as well type of jobs. Or a new board.
Mk is divided on silent switches and o-rings and such. Some are all about the clack and trying the lessen that is a crime, while others will roll o-rings and buy silent switch boards. I have two boards, both linear, with o-rings and one with tactile clears, heavy step browns, with out o-rings. I like both for different things. I want to try the cherry silent switches.