Amazon does not remove firmware files from their server.
They only remove the old links from the "device page".
So you could say that Amazon runs its own archive.
The bad links you mentioned are all to "factory-use-only" firmware versions used in jail breaking, not customer-use firmware builds.
If you went to the PW2 device page now, you would find the current firmware's URL:
https://s3.amazonaws.com/firmwaredow..._v2_5.10.2.bin
but instead you want a less current firmware, just change the firmware numeric field in the URL (for PW2-5.9.6):
https://s3.amazonaws.com/firmwaredow...e_v2_5.9.6.bin
Hint:
If you quote this post, you can see the full URL rather than the shortened version.