I got an answer for y'all:

The clamps on the header-to-midpipe size are 47-51mm (or something to fit a 1.5" I.D. hose, ranging 1.85" - 2") and brand used is commonly Mikalor.

If you're on the hunt in the US, I'm not finding them readily on Amazon but I'll keep looking.

Edit: Bam - $10 from Amazon.