Monrovia carries Pyrus calleryana 'Capital'and Pyrus calleryana 'Whitehouse'. You should be able to find them at the following retailers:
SUMMERWINDS NURSERY #72
861 E. EL CAMINO REAL
SUNNYVALE, CA 94087
(408) 245-4532
SUMMERWINDS NURSERY #59
1491 S. DE ANZA BLVD.
CUPERTINO, CA 95014
(408) 996-8355
YAMAGAMI'S NURSERY
1361 S. DE ANZA BLVD.
CUPERTINO, CA 95014
(408) 252-3347