I am not aware of any Vans operating from the airport terminal, unless this is where the main transit terminal is now located.
If there are no vans there, just take a trike from the airport into town and then take the public shuttle van to Roxas like has been mentioned, then you take another shuttle van from Roxas to El Nido.
There will be some vans going from San Vicente to El Nido, but they will stop at the Roxas transit terminal anyway, either to drop off passengers, or take on others for the trip thru to El Nido.
During our next trip to Palawan i will be visiting many of the popular tourist locations in Palawan, and i will be compiling a log of all available transportation to and from each of these locations, and posting it here in this forum.
Cheers