During the golden years, Legacies sent recruiters to local FBO's trying to find candidates (and were often turned away), and frequently hired PPL's and Comm/SEL's. I personally know of several now-retired Pan Am guys who earned their Comm/MEL ratings in a 707 back in the 60's. Funny, I didn't hear the wailing and nashing of teeth back them about not being qualified, and trust me, those birds were much more challenging to fly than these flying CPU's around today. There was no such thing as apprenticing for a "regional" carrier then, you either got military guys or very low time civillians flying large jets. The equivilant of today's "regionals", what were known as "non-scheds" were primarily manned by guys with incidents and DUI's on their records.
You won't get quality applicants for these positions because the lifestyle sucks. I have no problem finding tons of 5-8,000 hr regional FO's to fly for us doing charter work. Why? Few overnights, good pay, and a focus on professionalism and QOL. Things the airline industry has given up on. I have no problem finding guys to fly a PA-31 who came from the Regional world, mainly because I pay better and treat them better. (Please don't PM me, I only hire personal referrals).
Oh yeah, few unions in the 135 world, and our workplace is considerably improved over the 121 flying. Go figure.