Have you looked up your exact toilet? My old toilet lid broke and I found a replacement pretty easy. I know your situation may be different.
For single flush, they are all kinda the same or similar internals as far as flushing mechanism. You can replace the pump etc real easy.
Every 2 button toilet I've seen are all pretty much the same or similar. They aren't really that far off from the old style really, it's just push buttons instead of lever and float.
I don't specialize in plumbing sorry but Imo, you should be able to find whatever you need. You'll either get exact matching parts based on model, or some aftermarket thing. Your model number is usually inside tank on a side wall printed or stamped.