How exactly are you " backing the source folders to other hard drives as a safety measure" ?
Have you been backing up Lightroom catalog regularly?
Check that your secondary harddrive is working fine.
Nit sure what and or how you are backing up your Source files but it is best to do that with Finder to simply Copy your images from one external drive to another including all your folder structure (that is if you have a folder structure).
The reason you are having problems with images disappearing could be Mac OS X is slow to connect external drives. More so if the external drives you are using are powered by the USB port they are plugged into. Mac computers, especially notebook Mac's, don't put out a lot of power to the USB ports. Even if the external drives have their own AC power adapter OS X is slow finding and connecting external drives. OS X also has a bad habit of shutting down external drives or putting them to sleep after a relatively short period of time even if those options are unchecked in the system preferences.
The catalog is the catalog, it is not the location of your images. Images can be stored anywhere and not affect the catalog file in LR. If you Sort your images by Capture time all images will be displayed in chronological order no matter where the images are on any drive or in what folders the images are in on any drive or the name of the File.
I am wondering if anyone has any advice on if this mess is fixable. All I want is to access all my photos and edits each time I go to LR. Currently I now just spend 30 mins to an hour trying to find the correct hard drive / catalogue and usually just give up in disgust.
Yes it's fixable, but it will take some effort. There's no automatic fix. It would help if you understood how Lightroom interacts with your images ... Lightroom only stores a reference to the image location on your hard disk, it does not contain your photos. So it must know at all times where the photo is located. If you move it outside of Lightroom, or rename it, or disconnect the hard drive, then Lightroom can't find your photo. If that happens, the solution is to reconnect the photo inside of Lightroom using these techniques: Adobe Lightroom - Find moved or missing files and folders
Once this is fixed, if you leave your hard drives plugged in, you won't have to find the correct hard drive. If you have to disconnect the hard drive for a good reason, then of course you'd have to reconnect it before you open Lightroom.