Sure, I remember "The Invaders". I was a kid then and it scared the daylights out of me. More recently people have said it was an allusion to Communist infiltration of the US.
That show was made by Quinn Martin Productions who also made the famous 70's detective shows Barnaby Jones and Cannon (these were part of the same era as Columbo with a detective with some sort of eccentricity, i.e. Columbo is slovenly and apologetic,
Cannon is fat and a bon vivant, Barnaby is old and orders milk in a bar). So far as I know, no QM shows have appeared in DVD.

Yeah, I loved The Invaders when I was a kid as well.

Your right, the programme was deliberately trying to tap into prevailing cold war paranoia and the interest in the then space race.

It recently was re-rerun in the UK in the middle of night, it still by and large stands up to day - though some episodes are clunkers.

My understanding is that it is a problem with the Quinn Martin Estate and the TV company who currently own the programme. Some episodes appeared on video in the 80s but Martin's death seems to have prevented the various parties coming to some sort of agreement.

It's probably the reason why other Quinn Martin shows have not had a DVD release.

www.20six.co.uk/jiltedbarfly