Check the upper left corner of this page. This is a SanDisk site. The links are from the SanDisk server, so the firmwares are indeed here!
You can substitute the version number (last digits) in the current firmware link, e.g. “18a” in place of “29a”, and you can access the archived version, if you wish. SanDisk is very helpful in holding the previous versions on their server.
Having the older builds of the firmware is quite useful in troubleshooting, plus if a feature you liked in the previous build is your cup of tea, it’s still here.
You can, if you wish, download a copy of the firmware (present or earlier) and save it on your hard drive.