You should be able to cast your int to your enum value and then use reflection to get the StringValueAttribute.
Something like this:
MyEnum myEnum = (MyEnum)myInt;
FieldInfo fi = (typeof(MyEnum).GetField(myEnum.ToString());
StringValueAttribute[] attrb = (StringValueAttribute[])fi.GetCustomAttributes(typeof(StringValueAttribute, false);
return attrb[0].Value;