Hi, !
I am not aware of a surefire way to get a properly trained service dog for free, but I do know of some options you can look into. I can only provide so many links per post, so I will try to share the best ones I find.
Here's one reputable program -- https://canine.org/. And here's another -- https://www.ksds.org/. And another -- https://k94life.org/. Be aware that the waiting list for a companion dog can be very, very long and the application process can sometimes be rigorous. There are other reputable organizations, so let me know if you would like me to share more links.
I hope this helps and gives you some place to start.
Best, Erin, Team Member.