Where do I find the value of vintage audio equipment and best way to sell

This is my first time posting information regarding vintage home audio, so I hope I am in the right place.

My father was a vet and while overseas during Vietnam he purchased audio equipment. I am trying to determine the value of the equipment and find the best way to sell them.  I have all of the original purchase receipts, warranty certificates, and shipping records (both from the Japanese company shipping and the pick up once stateside).  I had them professionally cleaned a couple of years ago and they are in great shape.

He purchased the following:
Akai 1800D-ss Reel to Reel with 8 track and recording microphones
Dual 1229 turntable with retractable wood encasement
Sansui QR-6500 Receiver
2 sets of Pioneer CS-99A speakers