Guide books and tour companies mention about travel (or trip?) cancellation insurance, because of the short travel season in Alaska (and hence strict cancellation policies). Whom do we purchasde these from? From tour providers or other insurance companies? Please help with tips/suggestions. Thanks.

Start your inquiry here <http://www.insuremytrip.com/>. I am sure you will get a lot of good suggestions from other Fodorites.

Please do NOT purchase your insurance from your tour providers. If they go out of business with no notice, you are out of luck. Buy from an independent travel insurance company.

Travel Guard & Travel Safe are good

American Express offers a package also -
I'd look at a few of them and compare prices for what you want to cover -
air, hotel, total tour, emergency medical evacuation, etc, etc.

I also would not get it from the company providing my tour -

First, you have to evaluate the most likely reasons you would be unable to go and determine whether those reasons would be covered. When purchasing - be SURE to carefully read the exclusions.