And why bitch about Raven Guard? I'm happy with the new codex and have always run Raven Guard as my chapter. And I don't think the Forge Worlds and such hold their STC's. So most of the "more recent" Imperial tech upgrades would really need you to crack the Mechanicus Archives on Mars, I think. where the original STCs might be. At least if I was the Mecanicus, I wouldn't let anyone but the Mars Forge keep orignials.
As for new converts such as Astral Claws, or even just a fallen chapter, sure at the time of the fall they'd be modern equipped, but over even a few short decades, without Demon Forge support, their non Heresy equipment would break down and fail due to lack of parts.