there are actually a number of single letter domains still out there to reg , just not in the latin alpabet , ஜ.COM is one i own from the tamil alpahbet
These are from the kannada alphabet , which i also have
ೡ.COM
ಌ.com
ಬ.com
I have some from the runic alpabet , but they are so uncommon they dont appear on a website unless it has a runic language pack or script i think
the following scripts: Latin; Greek; Cyrillic; Armenian; Hebrew; Arabic; Syriac; Thaana; Devanagari; Bengali; Gurmukhi; Oriya; Tamil; Telegu; Kannada; Malayalam; Sinhala; Thai; Lao; Tibetan; Myanmar; Georgian; Hangul; Ethiopic; Cherokee; Canadian-Aboriginal Syllabics; Ogham; Runic; Khmer; Mongolian; Han (Japanese, Chinese, Korean ideographs); Hiragana; Katakana; Bopomofo and Yi , can all be registered and do contain opportunities to reg a single character domain ....... but not for ever