Spawn Enemy Attacks (SEA) by Enigx     The system creates random enemy attacks on SPECIFIC ROUTES placed on the map from the editor during mission editing. Just place empty markers to set one or more routes and run the script whenever you need. You can set the number of attacks and the time between them.
Especially useful for defining specific directions and waypoints, previously positioned on the map, from which you want the AI units movement to come.
Armaholic Spawn Enemy Attacks (SEA)   Hey, it seems Armaholic has been shut down!! 
Alternatively, I added the file to this link which uses a personal external website (completely unrelated to the Arma game).
Features: Infantry attacks using vehicles or not Waypoints previously placed on map for specific directions Full control of routes to be followed by units Multiple waypoint routes Fixed or random selection of routes, units and vehicles Single or multiple attacks organized in a cycle with selectable duration You can start, stop and restart the cycle at will Possibility to activate the system whenever you want from ACE self interaction menu SP and MP compatible
Installation / Usage:
For instructions and information of how to use the SEA please refer to file SEA_OpenMe.sqf.
Mission example included in zip archive.   Credits & Thanks:
Thanks to Armaholic Community.   Changelog:
First official version 1.0