Cat Town in Oakland, CA actaully focuses on and has pioneered a lot of work with "Forgotten Kittens" (the under-socialized or totally unsocialized cats ages 3-9 months old), so I highly recommend reaching out to them! Their cat cafe is 100% populated by Forgotten Kittens who have spent time being socialized and are ready to find homes.
Their step #1 though is getting those cats in foster homes for socialization (and of course training the fosters/providing resources to start interacting with the cats). They do have a few cozy and quiet rooms onsite where they do some socialization, but ideally they send the cats to foster care.
I attended a Maddie's Apprenticeship there a couple years ago and attached some of the training resources (plus a couple photos related to their Forgotten Kittens).
#PetBehaviorandTraining