There is a wonderful product by RNK Distributing called "Quilters Select Fabric Prep". It is their new quilting products line endorsed by Alex Anderson. This is a feather weight fabric that fuses to the back of your fabric that adds a light support to the fabric to help relieve distortion, raveling, puckering and runs. (I am typing it right off the package). It is NOT a stableizer in the sense that you would use it in embroidery, but it supports your fabrics without adding bulk.
I fused it to the back of some silky fabric to add support before I cut it out. The item was to be embroidered, so I did use the appropriate stableizer and the jacket turned out beautiful. It was not stiff, but retained its softness and drape.
This can also be fused to the back of your finished machine embroidery to keep the "itchies" from little bellies when you embroider those dreaded baby onesies. Or any other itchy labels/seams/etc.

I am on the west coast of Canada so really can't recommend a source for you. We have a Michael's craft store within an hour's drive and I have found some cute charms there.

"Home Sew" catalog has lots of charms for sale and I bought lots at quilt shows.

I love the idea of batiks. The varied patterns would be perfect to represent the topography and color variations of a map

Would the silks still ravel if you use a thin type heat and bond? Someone on this board was saying that there is a thinner, lighter adhesive that is out now. I can't remember what the name of it was.

Just my opinion, but wouldn't this quilt work out better as a wall-hanging rather that a throw quilt? It would be easier to see and you wouldn't have to worry about cleaning it so much, and the threat of unraveling the countries would be almost not existent. And who want to unravel a country? LOL

What a great quilt that will be. Here's a place that sells tons of charms for low prices.

http://www.jewelrysupply.com/charm.html#

Would this work for stablizing t shirts for a quilt? or would a light weight iron on stablizer be better?

I was web searching today for panels & I ran across this that might interest you.

https://www.fabric.com/buy/dc-193/mu...ap-world-multi

RNK recommends it, not as a stabilizer, but as a fabric "prep", meaning it is not a true stabilizer because it will not hold embroidery stitches. It is intended to add body to the fibers to keep them from moving. But since you would be stippling or quilting the tshirts, could not see why you could not use it. It would be worth the try. It may not be cost effective, as a featherweight iron on interfacing would be less expensive....especially when you may have 20 to 50 tshirts squares that are sized up to 18 inches. And can use a coupon for Joann fabrics or find a deal at Walmart or Hobby Lobby.
I use most of the RNK/Floriani products and find them to be excellent. There are videos on their website about every one of their stabilizer/toppers/batting. Also on their new line of quilting products endorsed by Alex Anderson. (Love the bamboo batting and the wool batting)

If it's going to be a wallhanging, silks or other "luxury" fabrics would be okay. If it's for a throw, probably not. they often don't wash as well as cotton. How does she want to "mark" the places?