Where can I find metallic cord or metallic beading cord that is comparable to a No. 8 size Griffin® bead cord?
I see this in department stores and magazines but not for sale anywhere.
The stringing material that you need to look for is called metallic cord.
Some bead suppliers sell it in different sizes. I found one product at FireMountainGems.com.
It's called Metallic Braid Cord, but it is 1/8 inch, or about 3mm, thick. It is slightly stretchy.
No. 8 size Griffin® bead cord is 0.80mm thick. This is less than 1mm thick.
For a 0.80mm diameter you may need to look for thread rather than cord.
Some suppliers use the terms interchangeably, but in general thread is not as thick as cord.
For any bead supplier look for products under a category called stinging materials. You'll find different kinds of cords, threads, wire, ribbon, string, etc.
You may want to consider a metallic elastic cord. Again, it's a little thicker, but it's metallic.
Also, check out arts and crafts stores. Look in the sewing or trim sections for metallic cord or metallic thread.
Hopefully this information will satisfy your beading needs.