I purchased my booth from Amazon. First I figured out what size I needed and then started looking. Amazon had the best price and shipping was free (Prime). I purchased one that was 30" long and 10"- 12" deep. I cannot think of the brand and I am on my lunch hour at work so I can't go look, but Micro-Mark sells it. Amazon was much, much cheaper than Micro-Mark.
If I had the space I would just build me one that has no sides, but a very good filtered venting system. I was just able to fit my 1/350 KM Scharnhorst inside of it for painting.