Hasegawa makes them both, however they are both OOM these days.
You may choose to buy this one:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3144127449&category=2587
but the price is on the high side. Externally there are vwry few differences between the A and C models. A couple of ECM fairings on the back spine and the vertical blades in the Lerx that are now applied to all F-18 under service. Ejection seats are different too, but there also are C versions that use the early SJU. There are also several cockpit differences, but even the C versions are not all alike.
In on line model shops from france and spain you may be abble to find the A and B versions. But the expected shipping costs may be very high. Check too Hobbly link and Rainbow ten in Japan.
HTH,
Nuno