I said I'd post it one day and now is as good a time as any!
Here's where you can find each snail.
M1-01: Patrolling around Antares Station
M1-02: Hiding under the docking platform
M1-03: Hiding behind the HLD Cardinal
M1-04: Appears within 500 meters of the beacon about 30 seconds after it's been deployed
M1-05: Appears when VAC 3 is destroyed
M2-01: Exits the Adonia's docking bay if the Adonia and at least one other ship from it's convey are kept alive for the first section of the mission
M2-02: Floating among the debris near a CrossCube piece
M2-03: Exits the Cardinal's docking bay if the Tarik is destroyed
M2-04: Hiding in Hasting Depot's docking bay
M2-05: Flying near the Oslyabya in the mission prelude
M2-06: Departs the SS St. Lo's docking bay upon it's arrival at the end of the mission
M2-07: Exits the Lawson's docking bay if the Lawson is disabled
M2-08: Type SNAIL during the terminal CMD hacking sequence
M2-09: Randomly guarding one of the cruisers
M2-09L: Floating high in the debris field about halfway between the node and the station
M3-01: Hiding on the runway of the Intrepid during the mission intro
M3-02: Floating high along and ahead of the first freighter's flight trajectory
M3-03: Hiding near Echelon 1
M3-04: Will arrive from and guard the Intrepid if they player guides hostile torpedoes into a hostile cruiser
Good hunting!