And I am unsure of the other series, but Mechwarrior 3 had a flamethrower. Was a sort of useless weapon though. You could be mean with it. Arm yourself with 10 of those, a lot of heatsinks and a lot of leg armor. And you could run around and 1 hit KO mechs... down side is they went down with a big bang, damaging your own mech.

As for a blade, the "hydrolics" required to do that... And considering the mech armor could hold up to lasers, missiles, and guns. a sword seems an unlikely threat. Best case scenerio is mech walks up behind the other, smacks him in the arm and severs his arm, other mech turns around, now only metres away from the cockpit of the offending mech, opens fire.