I don't know of anything to specifically generate sequences like that, but you could probably come up with your own fairly easy. Afterall, it's just like using base-26 numbering, without any arabic numerals, i.e.
String makeStr(int num)
{
String s = ('a' + num / 26);
s += ('a' + num % 26);
return s;
} I didn't test this or anything, but as long as you have less than 26^2 strings, it'll get you the basic idea.