So I did substantial additional research on screw measurements and lingo. I also finally measured the TI's original chassis screws using my new digital caliper.
These are my findings on the original chassis screws:
-pan head, phillips, high-low thread
-head diameter: 5.3mm (or .209” aka #4)
-head height: 1.95mm
-thread (major) diameter: 3mm (or 15/128” or .118” aka #5)
-root (minor) diameter: 1.6mm
-length: 12mm or .47” (~1/2”)
-thread pitch (distance between adjacent threads): ~1mm
-threads per inch (TPI): 20
I also found a wholesaler with a detailed fastener product website. I called them, and the salesperson was kind enough to send me 2 dozen screws for testing. I believe I've found a near-perfect match! (See photo.) Just for good measure, I've reached out to a couple of other folks to have them test these, too, but I'm about 99% sure they match just fine.
Assuming these new screws are confirmed a match, I'm happy to share some with anyone who might need or want them. (The cost would simply be 5 cents per screw + USPS shipping. Note I'm not looking to make any profit here. I'd simply like to make these easily available to other TI enthusiasts, since it was so challenging to accurately identify the size and then subsequently find a good wholesale source.)
To gauge interest, feel free to share your thoughts on whether you would like some and what quantities might make sense.