I am making a vacuum chamber for stabilizing wood. The container is a stainless steel pot. I was wondering if you could tell me what material I should use for the gasket, where to purchase it, and if I need to glue the ends together. Thank you.

I recommend BunaN or Butyl rubber.  If you have a tire shop near by, check in and see if they have a used tractor tire innertube.  If so, cut it open so you have a large flat piece and then cut a donut shape where the inside of the donut is smaller than the inside of your chamber and the outside is larger than the outside of your chamber.  Then you can simply lay that on top of the container, set your lid on, and start vacuum.  You may have to push down on the lid some to get it to seal but once it takes off, you are good to go.  If an innertube is not big enough to get a complete piece out of, I would order some 1/8" BunaN from the internet.  You do NOT want any joints in your gasket for the best results.