The CrackBerry forums are the single best resource for BlackBerry enthusiasts. There, you can find active discussions, guides, and links to firmware files. Look for threads titled "BlackBerry 10 Leaked/Beta OS". Community members are often the ones who preserve and share these files.
Throughout its lifecycle, the Z30 received several major software updates. Finding the right version depends on your specific needs for application compatibility and system stability. BlackBerry OS 10.2.x Blackberry Z30 Firmware
There are several methods to get a new firmware on your Z30, each with different levels of complexity and data preservation. The CrackBerry forums are the single best resource
Installing new firmware on your Blackberry Z30 is a relatively straightforward process. Here's how to do it: you can find active discussions