Tom,
I got the manuals in CD form a few years back from eflightmanuals.com.Unfortunately,they no longer sell manuals in a CD format.However,I just checked and they do still sell a large variety of manuals in print form.If you're interested try this link:
http://eflightmanuals.com/
From the left sidebar menu,click on "Product Index"
From the page number menu near the top of the page,click on "Page 57"
Scroll to the bottom of the page and click on "YFM-1/A/B Flight Manual",which is the 4th from the last choice.You'll have to click on "Available Media" to get the price for the printed (only available)version,which is $29.95
I've recently purchaced a number of manuals in CD format from an outfit in New Zealand with excellent results.They have the YFM manuals via this link:
http://www.flight-manuals-on-cd.com/YFM.html
One other item with quite a lot of information including some pictures on the YFM series is the excellent book "Cobra! The Bell Aircraft Corporation 1934-1946" by Birch Matthews.This book also has very detailed info and a large number of pictures covering the P-39 and P-63 series.I highly recommend it.Unfortunately,my copy is in Oregon and I'm currently in Florida.I just checked to see if "Cobra!" is still available.It is,at least through Amazon via this link.
http://www.amazon.com/Cobra-aircraft-co ... 7927SR=1-1