Nestle NAN Pro 2:
http://www.nestlebaby.com/sg/nestle_baby_club/goodies/Collector.html#may
http://123.100.248.230/nestle/NAN_Pro_2_Sample.aspx
http://123.100.248.230/nestle/NAN_HA_2_Sample.aspx
You can try calling these numbers but may be outdated:
Mamil Gold - 18002653188
Enfa - 18003455213
Similac - 62786220 62776349
Nestle NAN - 68367116 look for Clara (request for goodie bag)
Friso - 64198484
Promil Gold - 6733-7666
Diaper Samples (may be outdated too, you can try to google for updated link)
Heinz : no website so need to call them at 63471700 for a free sample.
huggies : http://www.huggies.com.sg/
(you can sign up FOC as a member and choose which sample you want them to send to you.)
Goon : http://www.diapers.com.sg/help.php?section=freesample
(sign up as a member and they will send you a sample of your choice FOC)
Mamy Poko : http://www.mamypokoclub.com/frmMemberLogin.aspx?page_from=memdefaut
(sign up as a member and they will send you a sample of your choice FOC)