Nonetheless here's the list of the clubs / societies that I could find. If you know of other such societies in Singapore, just let me know and I can add to the list. This list is also somewhat weird in the sense that many of the addresses do not appear permanent. If you have their web addresses that would be even more ideal!
Association Of Singapore Philatelic - Jurong Point Post Office, P.O.Box 492. Singapore 916417. DID : 65-6261-2421 & Fax : 65-6266-2750.
Kreta Ayer Stamp Society - Blk 4 #03-115 Sago Lane, Singapore 050004.
Singapore Stamp - c/o Singapore Philatelic Museum (SPM), 23-B Coleman Street Singapore 179807. DID: 6337 3888.
Singapore Philatelic Society - SPM (see above)
- Zui Yui Stamp Club - c/o 14 Moonstone Lane, Singapore 328456