The choice of "a" versus "an" is based on sound, not spelling. I'm not sure what L/C stands for, but when letters are used like this, they are usually pronounced by naming letters: "El-see." Since the name of the letter L begins with a vowel sound, we use "an" in front of it.
"In order to spell 'italki,' I need to us an 'i,' a 't,' an 'a,' an 'l,' a 'k,' and an 'i.'"