altc and sungbeng are the two i usually call and ask.
also can go sgcarmart to look for used tyres in the marketplace.
only buy second hand if you scraping in less than 1 year. and only look for 80% tyre threads and no more than 2 years old. and look for good brands.
tyres are like the most important part of a car. seriously, from braking, to acceleration, to wet roads to cornering, to fuel efficiency, noise level, suspension comfort and even your ego. so don't save on tyres.
unless you are buying literally to scrap instantly, then please drive slowly to the scrapyard.