Actually middle linebackers are easy to find, you have to be willing to sacrifice. Every year between 4 and 6 pass rushers are drafted in round 1, on average about 2 of them pan out very well, and 2 of them fail completely.
The last 10 mlb/ilbs that have been drafted in round 1:
Luke Kuechly (DROY)
Donta Hightower (starter, but not great)
Rolando Mclain (bust)
Jerod Meyo (stud)
Patrick Willis (stud)
Lawrence Timmons (stud)
Jon Beason (stud but injury problems)
Chad Greenway (stud)
Bobby Carpenter (bust)
Jonathan Vilma (good)
2 outright busts, Hightower can't be projected yet and plays mostly SLB. Beason have run in to injury problems and Vilma is a douchenozzle but both are good players.
In the top of the 2nd round you have guys like Demeco Ryans, Paul Puslysny, Curtis Lofton, Dqwell Jackson, James Laurinaitis. If you want a MLB you find one worthy of a 1st round pick and you are pretty sure he will turn out to be a decent player, but there aren't many players like that. Taking a MLB in a lower round is a much worse proposition since LBs are so relatively easy to project.