Spawnmaster can do this...
Add into the mq2spawnmaster.ini file a line like:
[Servername.Charname]
OnSpawnCommand=/multiline ; /popup SPAWN: ${Spawnmaster.LastMatch}! ; /beep
And you will get a beep anytime a spawn being watched by spawnmaster spawns. If the particular mob you are looking for isn't in spawnmaster, you can add it with the command listed in the wiki - I think it's something like /spawnmaster mobname add. Just be aware that any mobs that contain a watched mobs name as part of their name, will set off the beep - so Fright also triggers on frightfinger - zoning into Fear itself triggers a string of beeps that goes on forever....