Hmm, I thought of one printed source for this stuff.

Mel Bay Presents Jethro Burns, Mandolin Player, by Jethro Burns and Ken Eidson

It's a book of tunes and exercises as played by the great Jethro Burns. I highly recommend it--Jethro Burns was a genius, a very innovative player, and you can glean lots of musical ideas by studying his arrangements and tunes. Among the exercises is a set of endings in various keys, although there's no corresponding page of intro licks, there are certainly some you can adapt.