Where are these ranges obtained .. web sites, etc? Is there an online source that publishes these ranges or are they obtained from listings?
Cap rates, just like sale prices are obtained from sources. The sources vary, and just like the confirmation process for residential, the sale of commercial properties must also be confirmed for accuracy.
Typically the sales price for commercial and residential properties are obtained from public records (in some states) or from the brokers/RE agents involved. The commercial property sales typically need more verification. Income information is not in public records, and some of the income and expense data in the listings are "skewed". You have to verify, interview, research and confirm.
If you do not do this you might as well guess. It will not be accurate.
You must know who pays what, who gets credit for what...ad finitum.
I remember a discussion with appraisers 160 miles away from me a couple years ago. They had apartment buildings selling for 5% cap rates. My market was 8.5%. Pretty huge difference in value.
You can get information from web sites like CoStar, or Loopnet, but they still have to be confirmed. Many times they are wrong.
Cap rates are obtained from extensive research and due diligence. That is one of the reasons commercial reports get higher fees, it takes a lot more time to do them as the information is not as readily available.