Some of the transient recorders might have a trigger output that can be configurated to fire when there was an input trigger event
or when the recording is complete for linking transient recorders together.
Hmm... from your text, what you need seems to be a "trigger box" that contains a fast analog comparator triggering a bunch of "monoflops"
for generating individually delayed trigger signals for your scopes.
Of course, analog monoflops like 74HCT123 might have a considerable propagation delay, and digital monoflops built with counters would give you a jitter.
Edit:
Linear Technology application note
AN72: A Seven-Nanosecond Comparator for Single Supply Operation.
Texas Instruments
74AHCT123 dual retriggerable monostable multivibrators.