So, continuing to go over the car after I got it, the threaded inserts that the bolts/screws for the license plate to thread into are missing. Anyone know the correct terminology for these, and where I could source some replacements?

 

Check out the Help! section of universal parts at your local auto parts store. It should look very similar to the inserts that are found on the undertray and front lip.

 

Gotcha, I debated on doing that, but I wasn't entirely sure if they fit. I checked the Mazda parts catalog, and had no luck there. I suppose even if they don't they are cheap enough it wouldn't be much of an inconvenience. I appreciate it!

 

I've always called them 'captured nuts'.
As been discussed in other threads, if all else fails, a trip to the local 'U-Pull-it" yard for any 90's era MAZDA or pretty much any Japanese import car and you can fill your pockets with all sorts of fasteners. The interior is a great place to look as those have never been exposed to weather.