DivisoriaProbably the biggest source of alternative brick toys. The prices here are usually at wholesale prices. Look for the toy outlets in 168 mall. If you are willing to walk a bit from 168 there is also Anding's Toy Store which has the lowest prices. The only concern in going to Divisoria is the amount of shoppers who are usually there as well as the lower security in the area.
The Landmark Toy SectionThe Landmark toy department has an unusually wide selection of Lego models available. But aside form Lego they also carry a dizzying array of alternative brick toys. You can usually find a smattering of COGO, Sluban, Enlighten and Ausini brick sets in their toy sections
They now have a wide assortment of the Sluban/Ausini military sets. Great tanks and planes. They also have a huge section now dedicated to China brick toys
A Different Bookstore/Fully BookedThe sister bookstores usually carry Sluban and Enlighten brand items. Shops are found usually in malls in around the metro. Major stores are found in Bonifacio High Street and Alabang Town Center.
Toys R Us/ Toy KingdomNormally you'd find a small selection of Sluban sets in these major toy stores.
These are the major areas I can remember that can fulfil your hankering for brick like toys. I'll add to this list whenever I find a new source.
Greenhills Shopping Center UPDATE (9/8/2013)The lobby area of Shoppesville usually contains booths that sell a smattering of China brick toys of various brands
On the second floor of Shoppesville is a small corner shop called Regina Gift Shoppe that sells a Divisoria like selection of China brick toys including a great assortment of Star Diamond sets.
The tiangge area of market market! right across the Pearl Sellers has a host of booths selling China Brick toys!