OEM gen 1 wheels are 14x5.5/45 mm offset and 4x100 BC. Hub bore is 56.4 mm. weight about 10.2 lb. with centercap.
WARNING: if you look to after market wheels pay attention to the wheel WEIGHT. Anything more than 10.5 lb will lose mpg.
Also check to see if the wheel dish clears your calipers.
TireRack is the only source I know that publishes their wheel weights. I think someone mentioned they have a kosei 14x6 or 5,5 wheel that weighs about 9 pounds that will work. cost about $120 each, which is very low for such a wheel; most cost $300-$400 each.
PS going bigger diameter or wider tires will cost more mpg than a 12 lb wheel.