In the Kstars Mac Profile Editor there a driver for the Rigel systems N-Step focus motor listed I selected. But apparently its not actually in the Mac version, as it (sadly) won't connect to my Rigel Systems motor. Is there a way to add it to Kstars or plans to add it in the near future? I've checked cables and connections.
Note that I am not an expert on nStep and I don't know the specifics of that device. I can provide some context however because I build the Mac version of KStars and I have worked to fix issues with a number of drivers.
The INDI nStep driver is definitely included with the Mac version of KStars and it is the "Mac version" of the driver. Note that there is no specifically Mac version, as INDI drivers are cross platform. The driver on your Mac in KStars was built on my Mac specifically for Mac computers however. I can't say 100% that there are no issues with the nStep driver since I don't know about that device or driver specifically, but I can tell you that most likely that is not the cause of the problem.
Many Focusers and a number of mounts use Serial commands to talk to the mount for focuser. As such, you would either have your own USB Serial adapter connected to your Mac or the USB Serial adapter might be built into the device. The INDI driver sends those serial commands. Do you have whatever driver is needed to use that USB Serial adapter installed on your Mac? I know that for my Moonlite Focuser, It has a built in USB-Serial adapter and I have to install the FTDI driver. For my Losmandy G11 Mount, I have a Prolific USB Serial adapter and I have to install their driver.
I am sorry I don't know more about your specific device or if this is not the problem, but I think if you check into it, you might find a USB Serial adapter and you should be able to find a hardware driver for it from the manufacturer.