Infiltrator-style special forces are more of a strategic asset - I call them the kind of people who get really dangerous when they disembark from their 'Mech. If they are 'Mech-qualified in the first place.
Using these people in a stand-up fight, like sending the Death Commandos against Kathil, is a crazy waste of resources. (Granted, the Death Commandos were rather portrayed as elite MechWarriors early on when Stackpole wrote Coupé, and only later gradually morphed into elite James Bond-style infiltrators as the evolution of the BT universe progressed.)
On a gameboard, I reckon you would best represent those units as a hidden regular infantry unit with a TAG. Depending on the mission setup, they might use the TAG to play havoc with guided ammunitions of all sorts, or the mission objective might be to extract them under fire.
Off the top of my head, a quick rundown of possible candidate forces:
Davion: Rabid Foxes (portrayed as infantry; not sure if they ever use 'Mechs)
Kurita: DEST (portrayed as infiltrators, infantry and 'Mech forces)
Steiner: Loki (portrayed as infiltrators)
Marik: Dark Shadows (SAFE special ops 'Mech unit, drawn together from MechWarriors from other line units on detached duty; this being SAFE, they were duped and wiped out during the Jihad)
Liao: Death Commandos (infiltrators, 'Mech forces), Warrior Houses (infiltrators, infantry, 'Mech forces)
Wolf's Dragoons: Seventh Commando (infiltrators)
ComStar/Word of Blake: yeah...