I know that the stressed syllable in any given word is the second to last, but it would be helpful to hear a set of vetted examples (and also incorrect examples, if possible).
Jen estas iom pli ol mil frazoj kun sondosieroj. Mi aŭdis plurajn kaj ili estas tre bonaj kaj diversaj. Bedaŭrinde tie ne estas frazoj kun erara akcento :-)
There is a website, forvo, that has over 20,000 pronounced words by Esperantists from around the world.
You might want to try this pronunciation CD with recordings by John Wells who was previously a professor of phonetics and president of the UEA.
I would say that one of the best pronunciations I ever heard is the http://pola-retradio.org/
On the same time I have always to mention that the perfect pronunciation doesn't really matter in Esperanto. As long as you can get your thoughts across, you're good.
I would assume the Esperanto Duolingo course to have correct pronunciations.
There was an interval of time during which regular conference telephone calls were held among a few Esperantists, with discussion on various topics, partly, or perhaps mainly, in order to provide model pronunciation and stylistic guidance for posterity. This was done as part of the internal activity of Esperanto-USA, and the recordings should be in the archives of that organization. The interval of time in question was, so far as I can remember, from sometime in the late 1990’s to sometime in the early 2000’s, and was spearheaded by the Esperanto-USA commissioner of education (at the time) R. Kent Jones (since deceased).