ID has not shipped with any templates since CS5, and those were mostly made in even earlier versions. You can find them at InDesign Secrets, or by a google search, but I don't see much point -- a trifold brochure is pretty basic.
The earlier version of InDesign templates are available via InDesign Secrets:
They include a tri-fold leaflet template. Curious it should have this name as there are only two folds and six "pages".
If your leaflet is to be a roll fold (as opposed to a zig-zag fold), ensure the last page, that is on the right-hand side when you're looking at the inside of the leaflet, is slightly narrower so it tucks in when it's folded.