The birthday celebration balloons are still available in all the Poptropica Common rooms. And if you try a lot of times you can still find the blue birthday balloon with the big number 3 on it. When you find that balloon and click on it all the balloons in the room will go POP! and you will get a special ultra-rare costume. It’s the blue birthday costume in the picture above. The hat looks totally funny with the big number 3 perched up on top. You also get a little party noisemaker and when you press the space bar your character will blow into it.
Finding the blue balloon is really hard because it only appears one in a while. To get it you either have to be really lucky or just keep entering and exiting the common rooms a lot.
It can appear in any of the Poptropica common rooms which are all on Main Street on the islands, also known as the starting zones. So pick whichever one you like the best and keep trying.