Here is it's youtube channel: https://www.youtube.com/channel/UCcRhvOOOoEzmCNB7_D5K6Cw
But note, that it is divided by subject not grade, and under a subject you can find the level, also note that the level is specified in many of the video titles, but not all of them are specified, and if I am not mistaken it goes up to the ninth grade, so if you don't want to scroll through all of it you can just pick one and listen :)