As of February 2012 there is only one known confirmed registered ApHC (Appaloosa Horse Club) registered silver. A few others have been suspected but no others have been confirmed.
2008 Bay Silver ApHC mare
(Champs Guthrie X Duchess Dancer)
Ee AAt nZ
Unfortunately, Khepri, didn't get her spots but she can still be bred to a few spot or snow cap for guaranteed spots with 50% chance of silver.
Bred by Dominique Dupon
Owned by Ken & Monique Matson of Safyre Sporthorses
UPDATE: In August 2012 Khepri was presented to the ISR/Oldenburg N.A. for warmblood breeding approval. She earned 105 points - a Premium score !!!
No known stallions