OT – Book search

I have read with great interest several books on the South East Asia War air operations. I have seen reference to RF101 and RF4 operations but can find no books on the subject. Likewise the “college eye” EC121 operations, and the missions to monitor the sonarbouys dropped on and around the Ho Chi Minh trail.
Can anyone help please.
Most book searches ABE, Amazon EBay etc require either title or author there isn’t any obvious way to search on subject.
Any pointers much appreciated.
Thanks in advance for your time and trouble.
Be lucky
David