I found a used Chase Harper that works well, shaped just like a shoe box with a magnetic bottom rather than side flaps. I have no idea was model it is, or was, but you might try to look for something similar. Ebay has a ton of magnetic tank bags, Amazon too.
I love my Cortech Super 2.0 Low Profile. It expands from 5L to 10L and has nice organizer pockets. I also like that it has a bright red lining so it’s easy to see everything inside. It seems as well-made as my Kreiga backpack and it looks nice on the tank. They make larger sizes too, but this size is perfect for me.
I almost bought the Cortech bags, but I found some at a local dealer last year and hated the red cotton lining. Looked like it would pill up immediately once you stuff velcro cuff gloves in there a couple times.
Not sure how many liters it is, but it's medium sized I'd say and sits below the instruments. When expanded you get an extra 2.5" deep. It'll easily fit a bunch of 20oz waters + sandwichs. I've used it for shopping runs, and 1000 mile rides. More expensive than most, but has a lifetime warranty. The magnets are well positioned for the Scrambler tank, they all land on steel surfaces not the aluminum panels or gas cap.
With magnet bags you'll want to make sure the tank is clean because vibration will grind up the paint. The early Scramblers had super thin tank paint. Not sure if they still do, but mine has barely begun to wear in a few spots (above the gas cap mostly). Doesn't really bother me. I'll get to repaint sometime.
Related: those are the larger Kriega bags. 100% recommend that system.