What some bolt manufacturers will specify is "OEM +XXmm" the XX being the spacer thickness.
This is a good source my Googling turned up:
Otis Inc LA
RAD USA Direct
toll-free 855.OTIS.INC (684.7462)
toll-free 888.RAD.BOLT (723.2658)
international +01.310.995.8939
fax 310.305.0465
otisincla.com Home
Home