You’re missing the tiny, tiny detail that you need a fuckload of skill to make those weapons. This, unsurprisingly, ups the rarity a lot.
We’re talking about players being capable of making deathmobiles far sooner, we’re talking about being able to craft complex chemicals and even mutagens at relevant skill and time investment, heck, they can make CBMs sooner, and if you don’t have endgame survivor armor by then, you’re pretty damn close.
And exactly how many weapons do you expect the player to ever want to make? Because by the point where you can even build a forge, let alone have the skill to make those blades, they’ve probably looted a couple dozen cars, and this number goes up if they’ve gone scavenging for parts for their deathmobile. I’m sure there’s more than enough quality steel there to make as many weapons as the player could possibly need to arm a faction.
The scavenging hunt you’re suggesting for good steel would just have no effect whatsoever.