Looking for Firmware 5.5.1C.0 WC9500 controller upgrade

I like to update the firmware oy my WC9500 Controller. My current firmware is 5.5.1.4 I like to update to 6.5.1.11

In the release notes I found the information, that I have to update to 5.5.1C.0 first. But this firmware I can not find anywhere.

The controller is working with WAC720 APs in a Layer 3 net.

In the release notes I found this:

Customer having WAC720, WAC730, In the Controller network:

1. Upgrade the controller to 5.5.1C.0 firmware.
2. Once the upgrade is complete login to the controller, and make sure that all the APs have come to the connected state.
3. Customer must wait for at least 10 minutes after all APs have come to connected state.
4. After waiting for 10 minutes, upgrade the controller to 6.5.1.11 firmware.
5. Once the upgrade is complete login to the controller and make sure all the APs have come to connected state, clients were able to connect to the network, and the controller network is up and running.

Does anyone konw, where I can get the firmware 5.5.1C.0 ?