Assuming you are going to be in CMB during daytime, you dont really need a travel agent if the only tickets you are booking are the straightforward CMB-westcoast SQ trips. You can always book on SQ's site, then go to the CMB CTO and pick them up. I've done that and its quite painless. Costs the equivalent of $20 for the cab fare for airport-CTO round trip.

Others here have asked for their tickets to be available at the checkin counter, so I'm sure that can be done too.

On the other hand, for more complicated itineraries ....