Is there something listed somewhere that details when the holiday events are? I know there's some summer stuff but I thought they would have started by now. I tried Googling it and couldn't find details, I'm probably searching using the wrong terms.
your answer is only two tabs away from "forums" here on lotro.com, at the top of the page. Just click the "calendar" tab. Or if you prefer, here is the direct link: http://forums.lotro.com/calendar.php
(you'll notice you already missed the spring festival event earlier this month)
The next scheduled major event looks to be the 'Farmer's Faire' in mid-july
the problems with festival and other event dates is turbine dont usually announce them until a few weeks before theyre due to run, even the yule festival which runs through december 25th isnt in the calendar for this year and that usually runs around the same time each year
the best thing you can do is look at what happened last year which should give you a rough idea what will be happening this year although the farmers faire sounds like we may be seeing something different for this years summer festival