Andrew- Sorry to read this. A quick search: Boise Metal Recycling in Boise, ID | DexKnows.com
shows that you have many places in Boise that recycle. Something else to keep in mind is that you may be dealing with a large scale crook that will chop your frame into 6" pieces and throw it in a large bin for bulk scraping, so don't hesitate to call the yards that only accept larger tonnage amounts or require accounts.
I scrap off my job sites all the time, and it's an interesting trip for people watching when getting to the recyclers to say the least.
...another idea would be to see if any others tennants in that area have cctv, that may have video of a truck driving by with it on. That would at least help you narrow down some possibilities of who. If you did get a picture, show it around to the recyclers as the guys scraping, will be back sooner than later.