As of 10/21/2013 19:30 GMT, Krohkur has 2 days 8 hours to Mentoring Availability. As of this post, he is 47th level (meaning the only things he can't teach yet are Bagpipes and Moor Cowbell... he can teach normal Cowbell).
Minstrels can use a "Scribe Stance" skill with an item purchased from any Bard or Minstrel Trainer, allowing the Mentoring for an instrument to be "written" into a scroll, for mailing, as an example. (I think they can be placed in the Auction House, as well, so you may be able to pick up instrument skills there.) Note that the cool-down for the Minstrel goes to 10 (yes, TEN) days when Scribe Stance is used.
Here is the list of Mentoring Skills:
EDIT: Eeek... LOTROWiki uses transparent backgrounds on alternating rows of that chart. >.< Against our black background, black or dark blue text vanishes.
Workaround: Highlight the chart with your mouse, and you can read it in reverse video. - Krohkur