Whether you can use public STUN servers for commercial applications depends entirely on the licensing/Terms of Service agreement of the operator of said servers. Peruse those if available. If not indicated otherwise, I wouldn't distinguish "commercial" use from any other use.
There are many many implementations of STUN/TURN servers available you can set up yourself on any machine you happen to have (in practice that probably means an instance on AWS, Azure or the like). Search for and pick one you like. STUN servers use relatively little resources, while TURN servers typically need powerful CPUs and fast internet connections to be useful (they must relay the entire video stream as quickly as possible).
Operating such a server yourself may become expensive, depending on your usage. Using a commercial provider for TURN servers may be the better option; personally I've had good experiences with Twilio in this regard, but do shop around for other offerings.