Good source for downloadable audio walking tours?

I am a fan of self-paced audio walking tours, of the kind that some museums offer on electronic "talking sticks" as well as  audio city tours. They can be interesting introductions, or more specialized tours about architecture or history.

In the era of search engines and ubiquitous pocket computers (aka smartphones), I'd like to be able to download and call up relevant audio walking tours to learn more about places I'm visiting, or plan to visit, or even just as an engaging learning tool. Strange as this might sound, I've even enjoyed re-listening to this kind of tour long after a visit -- the audio helps elicit memories.

However, availability of audio tours is spotty. Very often, audio tours are only available in the places that they describe, like museums. (I say this is a waste of common resources, especially when it comes to tax-funded attractions like National Parks.)

Rick Steves has some great tours for some European cities, along with place-centric podcasts, and I've found a few others here and there online.  But what I'd like is to be able to browse and compare available (and in particular freely available) audio tours for cities, countries, museums, or other cultural attractions, so I hope someone can point out to me some kind of repository for them -- or better yet, a review site.  I'd enjoy finding ones available in more than one language, too, so I could do a bit of brushing up on some foreign-language comprehension.

(And No -- I don't want to keep my earbuds in place all the time when I travel. I just find it one very positive experience among many. With a well-produced audio guide, I can get some degree of local insight without joining a neck-craning crowd attached to an in-person local guide. I'd rather have a guide *after* I know a bit more.)

For anyone not familiar with this kind of experience, I recommend the audio tour at Alcatraz National Park (https://www.nps.gov/alca/planyourvisit/guidedtours.htm) and the above-mentioned  free tours from Rick Steves (https://www.ricksteves.com/watch-read-listen/audio/audio-tours).