Troubles with pncconf

Are you using mesa cards?
If not, you do not use the Pncconf, use the stepconf wizard.

This problem seems to have been mentioned a few times now. I can only suggest that you skip the test and ignore the missing-A and then correct the problems by editing the INI (and possibly HAL) files.

The INI and HAL files are what defines the configuration, PNCConf is just intended to be a helpful tool to get started, Unfortunately I think that the scope of the task became much greater than the author expected as shortly after he finished many more Mesa cards appeared.

You could also try starting with the pre-configured sample configuration. (open by_interface/mesa/hm2_stepper/7i43_big (or small). This will copy it to your linuxcnc directory, and then you can set the limits and scales directly in the INI.
(and the format is human-readable enough that it should be fairly easy to see how to add an A-axis)

You shouldn't need to download it at all. It is part of the LinuxCNC distribution.

Which version of LinuxCNC do you have?

2.7.8 is current, it might be worth checking with the update manager.