Well, that and dsmid's mirror linked on that page, which has the last couple as well. If you know the firmware version you want, you could also play with filenames and try to download it from Amazon. For instance:
http://s3.amazonaws.com/G7G_FirmwareUpdates_WebDownloads/update_kindle_5.4.3.2.bin
The only thing they change is the firmware number, and apparently even after they stop linking the old firmware at
http://amzn.com/kindlesoftwareupdates they still host the file and make it accessible.
Not owning a PW, I cannot be very judging

but I can say this -- many people are avoiding fw >= 5.4.2 since it comes with the Cloud Collections debacle.
In order to get there on the PW2 you will have to downgrade to 5.4.2 (an example firmware that can be jailbroken) and then go
HERE for the partition images for the 5.4.0 firmware, and manually flash them from the diags partition. There is a README there.

It is easier on the PW1, just use the provided fw5.3.9
Alternatively, just go to any old firmware, jailbreak, then upgrade again. The jailbreak will NOT be lost.
I suggest just using the earliest fw for the jailbreaking, it is easier than remembering which ones can be jailbroken

and if you will upgrade again right afterward, who cares?