You could try contacting MINDS (Movement for the Intellectually Disabled of Singapore) and APSN (Association for Persons with Special Needs). They both have programmes for youths and adults. Not all services may be available for expats (they have job placement and residential) but they'd probably be able to advise you at least.
Voluntary welfare organisations (VWOS) manage most services of this sort, and they are coordinated by the National Council of Social Services (NCSS). More about them here:
https://www.ncss.gov.sg/social-service- ... membership
