We created this zine and its sister zine Biz Against Russian Invasion, since most of the information is fragmented. In addition to trawing through news media, I use leave-russia.org and som.yale.edu. Both are sources for this zine.
One effective way is to ask shopowners for alternate brands and tell them why. The message gets passed to the brands we support and to thoe we reject. This method works for online grocery shopping as well.
The Yale Chief Executive Leadership Institute has also made it easy to contact companies to tell them to stop doing business in Russia, by providing their contact info at https://www.emailcontactukraine.com/ . We've posted this info in a comment