Maybe this is why the Wind Watchers fell to Chaos. Tzeentch was a more consistent supplier of goodies than these Forge Worlds.
But more seriously, I am just worried that the Inquisition and the wider Adeptus Mechanicus have already tried to put a stop to this in the 10 millennia since the Heresy and haven't succeeded. In which case, we'd need to have some special leverage or reason for this to work.
You're probably right.
A tentative plan for consideration;
Step 1: Go with Smilnay for the void ship specialty (especially since they aren't the ones being raging assholes to us, IIRC), do enough favors and shit to get all our current ships repaired and 2 escorts for each of them. As part of this, get as far into a full 10 companies as we can.
Step 1a: As part of this process, regularly send Marines out to secure favors and whatever tech we can find. Blue Marines need leverage badly!
Step 2: Go hard into producing a full range of what Volkite weapons we have, enough for our elites and a squad or two of the heavy weapons varieties.
Step 3: When they come begging for the plans after word gets out, make it clear that getting the plans is contingent on them putting aside this feud and forgiving any grudges, since we respect the Omnissiah and wish to ensure all his loyal children benefit from his generosity. Specifically insert "loyal" into that hammy speech, this particular crop of Techies is denser than a block of adamantium it would seem.
Step 4: When they predictably balk at this, just shrug and say that we are far too familiar with the damages of infighting to trust such valuable tech with those who cannot work together for the Imperium and the Omnissiah. Obviously this will be done in diplomat-weasel-speak.
Step 4a: Bait them a little bit more by sharing Volkite weaponry with our friends if safe to do so. Inquisitor Harker, the Blazing Wardens, and maybe those Gaelic-themed Sisters come to mind. Maybe one for the sector governor if we're still on good terms with him then.
Step 5: When they start getting uppity at how everyone else is getting these cool toys, put in a call to the Ordo Juris to sit on them long enough for us to hash out a treaty even these twits will not easily sidestep.
Also, completely random, is this supposed to be asking me for "submit vote and reply" even when I'm not posting an X'ed vote?
EDIT: Names are hard