Finding adequate guys for a 3-4 is very hard. Some of the players/positions are interchangeable in terms of size but their duties are what differs.
Examples:
A 4-3 DE and a 3-4 OLB are the same player physically, both are roughly 6'2"-6'4" 245lbs-265lbs, but that players duties are more extensive in the 3-4. He's gotta play standing up, he's gotta rush the passer and he's gotta cover. In the 4-3 he's simply just an edge player/pass rusher.
A 3-4 Nose and a 4-3 One-Technique might be the same player physically, both around 6'2"-6'4" 320lbs-345lbs, but in the 3-4 he's playing two gaps. In the 4-3 he's simply controlling the A-gap.
A 3-4 Defensive End might be a 3-technique in a 4-3 defense, but again, the duties are much different. These seem to be hard to find. You want a 3-4 DE to be long, atleast 6'4" and somewhere around 300lbs.
It's easier to find guys for the 4-3 because all you're really looking for is speed and explosiveness. Guys who can penetrate. When recruiting for the 3-4 you're looking for guys with massive balls. Guys who can take contact head-up, be a man, control the Offensive Linemen and shed blocks. It's a totally different type of player than a 4-3 guy.
Go back to that video clip of D'Onofrio yelling at our defensive player during practice. "QUIT RUNNING AROUND THE BLOCK! JACK'EM UP!" Our 4-3 bread South FLA players preferred to run around blocks.