All your question can be answered with SUUPERSTEEEL(echo).
Find it out today in the foundry! Go there now!
Well, that is the best metal.(up to Q.160)
Best electronics, armor Vests and gun parts are found in the shop of the very secret organization. VERY!(up to Q135..ish? Unsure.)
Very best metal PARTS(like tichrome spikes and steel blades) are found in the foundry shop near the enterence, what's her name?(up to Q.130)
The very best leathers can be found in the camp heather, with exception of ancient rat hound leather.(quality of each leather may very depending on which one it is)
But to really make use of them, you have to infuse them...
Institute to tchort shop also have quality items, but I THINK their items are little bit worse. Let's go with up to Q.125.
Of course, some part of the upper underrail MAY give you higher quality item than shop can provide. I checked.
And there is DC, where the most quality parts (I think, up to Q.160) can be obtained.
Foundry doesn't have any Super Steel. I don't know what triggers the progression of goods at merchants, but apparently it's not by level. Right now they have, at max, Q100-ish TiChrome. By "infuse" I am assuming you mean add optional components to the recipe. But if there is a specific "infuse" mechanic I haven't found it. Secret org? Well, I have access to Oculus and the hidden shop in Rail Crossing. Neither is particularly good atm. Camp Hathor is a good tip, had not tried them for a long time.
Overall it sounds like I am not triggering the progression of materials somehow. It sounds like maybe they go up by how far you've explored, and I am one of those people who clears as much content as possible before moving on. Maybe I just need to push into the later areas more aggressively.
You have to talk to people.
Like a guy who has super hot furnace.
Like, hottest furnace in the foundry.
So hot it could kill something...*wink wink* *nudge nudge*
As for lightningmonk's comment... Oligarchy shops lack quality a bit. I would say Q.120 to Q.125ish.
P.S: to learn about infusing, talk to the foundry metalpart shop woman afterword you have discovered supersteel.