User blog comment:Clockwork Tactics/Mech suits, are they allowed?/@comment-8395098-20140825153745/@comment-3993996-20140825170357

The only way to do it would be if you created a xenos race. However said race will probably be cliché, and mechs would still be a rare item.

However however.

If this Xenos race was wiped out by the space marine legions during the great crusade and this xenos race prior to its cleansing used mechs said xenos may be more original, although they would be wiped out by the Horus Heresy.