I constantly roll my eyes when I hear people say about their favorite NFL team, "Why don't they just bring in a pass rusher?" when it becomes clear that they don't get pressure on opposing quarterbacks. Some NFL teams regularly churn the bottom of the roster, working out players during the middle of the week that can help them with certain issues. What teams know they won't find is a competent pass rusher. Because they're treated like gold around the league.
To give you an idea of where pass rushers come from, I took the NFL top 10 in sacks from 2011-2013. I have left the list nameless and instead only listed draft position. The exercise is to show where teams are finding the top pass rushers in the league.
2011:
4th - 1st - 1st - 1st - 1st - 1st - 1st - 1st - 1st - 2nd
2012:
1st - 1st - 1st - Undrafted - 1st - 3rd - 3rd - 4th - 1st - 3rd
2013:
5th - 1st - 6th - 1st - 1st - Undrafted - 3rd - 4th - 1st - 1st
Totals: 18 of 30 positions filled by first round picks. 23 of 30 positions filled by top 90 draft picks.
If you want elite pass rushers you have to make them an organizational priority. Typically you have to prioritize them with high draft picks.
-los