On the internet you will find a lot of schemas for CAT & Audio interfaces. In this post you can see the result of the interface on a standard euro PCB board. With the ‘diylc’ software I had made a PCB design to reproduce the schema.
The nice alu-case (part number: ADG-D105.30.160) and the audio trafos (part number: P1200) you can get at Funk-Amateur web-shop in Germany.
The two cables to connect from the interface to the RIG are one old PC-keyboard cable and the other an connector cable for macintosh computers. The audio cables I had made from an single computer audio cable with mini-din connectors, who you can find in any computer shop. The RS232 is a standard cable (9 pins).
The software to connect the computer on the RIG is in my case the Ham Radio Deluxe. When you use the correct jumpers, you can use every kind o (small) management software you can find on the internet. You have to test the best positions ( RTS / DCD etc.)
In the download section you will find the corrsponding PCB file. The basic schema I found on the internet, I had made a few changes (ID LED etc.)