[BAccording to AikidoFAQ
Osawa sensei was given 10th dan after his death in 26.05.91, given post mortem by the Aikikai. Rinjiro Shirata sensei was also given a post mortem 10th Dan. This surprised me. You tend to forget about post mortem promotions.
Minoru Mochizuki 10th dan - given by the International Martial Arts Federation (IMAF) in 1979. There were also several other people who received 10th Dan by IMAF.
I think you can safely say
Koichi Tohei Sensei was the only one to receive a 10th Dan certificate from O Sensei. [/b]
KAMI : If you look back, you'll see that my list is about NON-japanese yudansha. That's why japanese sensei aren't included.