IC capable of transmiting IR over multiple pins
You're going to want an external driver for each LED anyway, in order to provide more current than an Arduino pin can supply on its own. There's no reason that external driver couldn't be a decoder/demultiplexer. You'd connect the Arduino's pin 3 to the enable input of that decoder, and use a few other GPIOs to drive the select inputs of the decoder. A 3:8 decoder would give you 8 independent LEDs that you can drive one at a time.