I know it's been addressed somewhat in other postings, but I don't have clear direction. The Thoughts Revealed mission is there, and I have completed it once, though it's been grayed out for some time as I have not completed the prior mission first.

As there doesn't appear to be a prior mission available, what's my plan to get more Genetarr Transmitters?

http://galaxylegion.com/wiki/index.php/ ... filtration

That is the first mission in the chain. You can use the "Next Mission" link at the bottom of each page to follow the chain; you have one of the missions before Thoughts Revealed available, so if you follow the chain in the wiki you'll see which mission it is that you haven't finished.