SO I started a new save, abandoning my 800hr game. Got to the freighter bit and found out that you need “Salvaged Frigate Modules” to purchase any upgrades (Up to 800 of them for the final Freighter Warp Drive)
Anyone find out where you can get em? I searched multiple Crashed Freighters but to no avail.
Ok. Scrap everything I stated earlier. The Salvaged Freighter Modules are not the same as Salvaged Data.
This will require investigation. I will edit the title above to help us find these Modules
One answer could be that these modules are obtained by launching frigate missions from your freighter. Specifically, industrial missions. Hope that is the answer.
The verbiage states that you use them at Research Station in your freighter, but I have do n’t have one (nor do I know how to get one.)
The verbiage also states that you get them from crashed freighters and frigate missions.
Yes, I believe you get those modules from expeditions, which can then be used in the ‘Research Station’ on your Freighter, which you find at the command center of the bridge.
Thank you. I admit that I have ignored anything but the frigate mission coordinator and the captain in that room 
I meant the actual bridge, where you have several consoles in a circle. I think it has been added there.
Quote from the Beyond Patch Notes:
Unlock freighter and frigate technologies from the freighter bridge.
Okay so just Cross-posting from another thread. Here’s how I solved my Salvaged Freighter Module problem:
The verbiage says you can get it from crashed freighters. I raided a dozen or so but no luck there.
They do come in frigate missions, but that’s too few and far between.
Fastest Way is to raid a Freighter group, but only the freighters themselves. If you attack the frigates or the Free floating Cargo Pods, each attack nets a negative standing with the system faction. But you can raid an entire freighter with only one faction standing loss; and easily make up to 10 Modules per freighter. Just buy the faction lads gifts afterwards to make up for it. 
When searching the crashed freighter did you activate the log from the terminal first and then select the crashed freighter mission that appears in the log? I find if I don’t do this I dont get the tech module. You also don’t get it every time but seems to be 1 in 3.
Which missions supply the freighter salvage modules?
I have sent out “one…two…,three…many, many, many”* frigate missions and to date have received no salvage items.
(*Pratchett)
I have a question. I purchased all the tech for my CS, and now I have a bunch of modules left over. When I eventually upgrade to a higher class CS, will I have to purchase that tech all over again? I don’t want to get rid of these, if I’m going to need them later.
Yes. It is no different than any ship you aquire. You must upgrade again.
Thanks @sheralmyst! I have my storage, crew kitchen, science areas, and greenhouse pretty well put together on this one, so I’ll just tuck these away in storage for whenever an S Class ship pops up. 
I wish we could use them to upgrade the slots even a tiny bit; I’m 1 tech slot shy of a full compliment of drives.
I’m extremely late to the party here, but since noone replied and I have asked myself this question quite a couple of time in the past, why not post an answer…
I have found that the likelyhood of finding salvage modules increases dramatically with the duration of the mission. Missions with 25+ hours of runtime seem to yield a salvage module somewhat regularly, though I don’t have any exact numbers (felt like 10% to 20%, but it’s impossible to tell from my small sample size).
I am unsure whether the difficulty rating itself, and the classification of the leading frigate might have something to do with it too, but what I do know is that even S-class frigates will not return any salvage modules from 3-star missions that last only a couple of hours.
Whew yeah I missed this thread, I posted something somewhere else…
Yes I also found the longer duration frigate mission regardless of type, do tend to return a Salvaged Frigate Module regularly. I recall a run of 3 missions in a row [over a few days] all returned 1 module each.
I used this to max out buying the available items/recipes.
Freighter Salvage did not work for me.