I don't seem to be able to get a mission that uses Complex Tech Parts, what do I need to do to unlock it ?

Be Rank 200 for the prototype engineering mission

Thanks, the wiki only said "Becomes Available Upon: Rank ?" , and I had thought some people under rank 150 had this mission unlocked.

I've updated the wiki so it now states level 200. I've actually already completed this mission, and the Prototype Engineering bays are probably one of the best rewards in the whole game.

Note that you can start getting Complex Tech Parts from the very first boss you encounter. All boss-provided artifact modules and structures can be scrapped for Complex Tech Parts, although the tougher the boss that drops them, the more the artifacts are worth.

Yeah, you should probably just keep the reward unless you've maxed out on it.

Oh I have a bunch of stuff that I can scrap since I have the max count, so it won't be too long before I can use this.

Lucky! I was saving up all mine, then two days before Dan added in Complex Tech Parts, I ran out of cargo space and decided to get rid of all my spares.