I have both a 29er hardtail and 27.5 full sus - In my opinion 29er is not so popular in Singapore mainly due to average height being lower than the likes of US or Europe, 29er in anything below 17" frame size 29er always had problems with toe overlap and the like, 27.5 is a better wheelsize for medium and below. Also on our kind of manufactured tight and twisty jungle type trails there is no big advantage to bigger wheels. My 29er rocked when I went to Western Australia and last year in Sabah and Sarawak on mixed logging trail and footpath in the mountains though. I can't see 29 dying out globally anytime soon. I don't buy tires in Singapore unless an emergency - what stock the distributor brings in and which LBS carries which type / size seems very hit and miss in any wheel size and they are all pretty much overpriced, I get them online, much better selection and you can always find them discounted by 40 to 60% over RRP.
29ers are fine on our trails, I ride mine at Ubin sometimes. If you are on a 17" or above frame 29ers are worth considering along with 27.5. To be honest there isn't a huge lot of difference; 95% of it is the rider not the machine.
The online stores that I have bought stuff from or price check are: Chainreactioncycles.com Wiggle.com sjscycles.co.uk (touring bike kit and other esoteric stuff that is impossible to find elsewhere) Starbike.com evans cycles Bike24.com
These are all eurpoean based they seem to be cheaper and have better shipping to Asia than the US stores. Some mates also recommend Taobao but I've never used it except to buy clothes and household stuff. Not sure about returns policies and the like with Taobao.
Locally I reckon Hup Leong are about the best bike shop, good stock and reasonable prices