Wirelessly power multiple LEDs with antenna?
The oscillator modules from Sparkfun you are linking to are not meant for RF transmission. You need a transmitter/receiver pair for each parking spot, assuming you are mimicking a system that would have distances of more than 3 feet. A Sparkfun module that you might look at is:  RF Link Transmitter - 434MHz WRL-10534. In a simple minded system you  could use transmitter/receiver pairs with four different frequencies. If all there spots were close to each other but far from the entrance, you could use one transmitter/receiver pair with different codes for the spots.

In the title of the question you use the phrase "power multiple LEDs". I assume you are not literally powering the LEDs, but signaling them.

For the very short distance in your model, I do not think much of an antenna would be needed.