I tried to find a matching CHDK version for my Canon PowerShot SX540 HS.
The tool ACID tells me:
No official builds are available for this camera
What could I do to get CHDK working on this camera?
Unless you're a developer with experience in reverse engineering firmware and prepared to put a lot of time and effort in, you can't use CHDK on your camera. As you can see from the CHDK developers page, the SX540 HS is colour coded black, which means:
Black - neither original firmware nor firmware dump is available
or in other words, it's not even possible to begin development of CHDK on the SX540 HS at the moment.