It can be bought from any computer shops but prices for different harddisks have increased a LOT because of floods in Thailand (december) last year.
It depends on which location you are staying. KL, PJ, Penang or Malacca ?
If KL, go to Low Yat Plaza, at No. 7 Jalan Bintang, Off Jalan Bukit Bintang, Bukit Bintang Central, Kuala Lumpur. Refer here..
http://plazalowyat.com/ Got many computer shops there such as Cycom Sales And Service, Viewnet Computer System, Thundermatch Technology, Compu-Zone. etc.
If, Petaling Jaya, go to Digital Mall at No. 2, Jalan 14/20 Section 14, 46100 Petaling Jaya, Selangor. Refer here...
http://www.digitalmall.com.my. Also got many shops there such as Jayacom Information S/B, Thundermatch Technology, ALL-IT Hypermarket, etc.
For many years I often travel from Pahang to KL and usually go to Lowyat Plaza... don't have any special preference so I bought from a few shops there since about year 2000... when only a few shops opened at that time. Bought a few WD My Passport AV (320GB, 2.5 in) at RM 230 each in 2010 BUT price
have increased a lot now so please check yourself.
You can also find people in this forum who sell it at ...
http://forum.lowyat.net/Memory&Drives. Be careful if you choose online payment and postage. Of course there are many reliable and trustworthy sellers in this forum but a few have been known to be conmen. I have bought from a few "trusted" ones by postage but I cannot let you know who, so find out on your own. Don't blame me if you got cheated so its advisable to COD (personally meet seller and then pay after checking items).
320GB most place no stock. 500GB and above plenty... that is why I ask.