Hi Brian,
As Matt said, I live in Manila. I'm primarily involved as a freelance/consultant instructor in tech/wreck/sidemount diving, but happy to hook up for a coffee and general chat to get you orientated, if you're around the Makati area.
The main dive shops I use are listed below, between them, they have everything you might need:
Makati Area:
Pacifica - Stocks and services Scubapro - has an excellent selection of bits and pieces.
Nautilus - OMS dealer with a good selection of gadgets and accessories.
Aquamundo - Sells their own brand, including rec and tec equipment, which is good quality and cheaper than imported stuff.
Aquaventure Whitetip - Apeks/Aqualung/Suunto dealer
TechAsia - Sells DiveRite and some other good tec stuff
(all of these are within 15 minutes walk from Greenbelt Mall)
Quezon City:
Divers' Point - Good stock of scuba kit.
Splash Underwater Images - The best place in Manila for underwater camera gear
Ocean Zone Explorers - UTD center, including UTD equipment.
Diver's Network - (Closed now, I think??) Lots of tech stuff.
There's plenty of active instructors in Manila. Most run training and trips - regular short diving trips to Anilao/Subic/Puerto Galera and occasional longer trips to further-flung locations, like Cebu, Coron or Palau. Choice of instructor/club might be dictated by the type of diving you want to be involved in. Also, there are regular social meet-ups by members of the Philippines Paradise Divers....and if you're into underwater photography, there is the "NUDI" photo club that meet monthly in Serendra/Fort (they have regular member photo competitions etc).