Being in Singapore definitely makes it harder to get batteries. Shipping restrictions are getting worse.
I don’t know of a specific company that ships there, but you might try nkon. They are in Europe.
If they don’t shop to Singapore, try this thread. Massive post on where to get lithium-ion batteries everywhere in the world!
You can also search the forum for other people in Singapore and send them a PM to see if they know of a good battery source.