iPhone 5 have been officially release yesterday in US, Australia, Canada, England, French, German, Japan as well as Singapore. At this moment, iPhone 5 users would already testing their phone or playing HD video with it. But for Malaysian, you may still need to wait for few weeks from now.
According to Sin Chew press, iPhone 5 will be most probably available in Malaysia by Oct 26 which is one month away from first release of iPhone 5. But since Maxis already announce the availability of nano-SIM by end of September, you can always purchase the iPhone 5 from Singapore and using nano-SIM provided by Maxis. I personally do not encourage to approach in this way but to officially get iPhone 5 from local telco.