Do these exist anywhere for your basic 30 round magazine? I'm looking to do some engraving and parkerizing to match the parkerized mags but as far as I can tell no one sells such a thing. At best you can find a rebuild kit with aluminum floor plates which sadly won't work for me; and I need 60 of them.

ASC and Duramag make stainless steel magazines.
ASC has an aluminum floor plate.
Duramag has some sort of ferrous plate. It attracts a magnet but to a much lesser degree than the stainless body.

I also checked a crappy painted steel mag.
The floor plate is ferrous, but thin and soft.
It is stamped "Made in Korea" with no markings on the body.

The only unmarked floor plates I have seen are aluminum Center Industries.

If you find a source for floor plates of any type, please post the info here.

For the quantity you need, have you tried contacting a magazine company directly? (D&H, ASC, etc.)  They may be willing to sell you bare ones discretely.

I had a few but gave them away to a member. I have a couple left but they are still attached to a mag.

Edited. Realized you wanted them unmarked.

hey dude i was scrolling in EE and found unmarked plates unsure if they are steel or not https://www.ar15.com/exchange/topicEE.html?t=2477929&f=24&type=1

they are out there , i have a 20 round thats old ,has the metal follower , unmarked floor plate