ArduPlane Firmware 3.2.1

I recently got an Ardupilot 2.8 controller board, which will not work with the latest firmware. I want to download the firmware from version 3.2.1, but the only ones that are available in that version is in ArduCopter. I tried uploading this firmware, and it worked, but now I am trying to install an airspeed sensor. When I try to connect the sensor under optional Hardware, the sensor is greyed out. I think its because you wouldn’t want to use an airspeed sensor on a Copter. Since I am working on a plane I need this functionality. How can I gain access to the old firmware for ArduPlane 3.2.1?
Thank you!

I think I figured it out, Everywhere it keeps saying 3.2.1 is the last firmware for APM 2. But that is only true for arducopter. For arduPlane it is 3.4.0