Rather late i suppose, but if it helps:
You probably want to try the Tetra chain of stores, www.uae-pets.com
They have branches in khalidiya and one on electra street and in almariah mall
I recommend the electra branch
You'll find some beautiful silver angels for 5dh (<$2 each), their plants are 5-10dh each (even got some huge crypts and hygro, great price, $1 pots of hairgrass!). They have the biggest range of filter equipment in AD, eheim, fluval, etc (but no aquaclear
) and some nice tanks and ferts etc.
No CO2 equipment, just as well you probably won't find any in the UAE, better trying to contact a fizzy drinks company for the regulator and tank they might have some. I believe there's an aquarium equipment trade show going on in a month in dubai at the crowne plaza, you might want to look that up.