Cross-CPU Communications
What you are referring to can be accomplished with a "dual-port RAM", which allows simultaneous access of the same memory location using on-chip arbitration logic.

They are available from 1KB to several MB, and are not cheap -- a 16KB device costs $30 in quantities of 1, and $22 in hundreds at Digi-Key.  Here is a datasheet for the device.  I assumed you wanted an 8-bit interface since you are interfacing one side of it to a 68008.  You can find more devices at Digi-Key searching for "dual port".