Just go to those clearout stores where they always display cheap Energizer batteries among other even cheaper batteries outside, for example ABC store at Bugis and Peninsula, that kind. They will have Philips and Osram and some other funny brands for you to choose from. But they're not very directional, so it depends on how you want to light your tent.
Oh, you can get clamp bulb holders on those stores too, to attach your bulbs to your tent, if you haven't already had a solution to attaching bulbs.