Not quite sure about your reference to Roman letters or do you refer to Roman numerals? Either way I am not aware of their use in reference to buses.

You should be able to find the bus to Jomtien/Pattaya at the airport.

In Jomtien the bus station/stop is within walking distance of Jomtien Complex at the FoodMart.

http://airportpattayabus.com/v1/

Easier if you just hire a car/driver for 1200 Baht.