I can see occasionally some Pentax DSLR users want to download the older firmware and program it back into their bodies for whatever reason(s) of their own. But the first thing they have been asking is where to get and download the older version(s) of the firmware?
Actually, most of those are still kept at the Pentax.jp server, just do it this way:-
1. The current and latest firmware is linked in each support page of the respective camera model, i.e.:-
http://www.pentax.jp/english/support/digital/firmware/k5_e113w.EXE is linked from the download support page for the firmware version 1.13 of the K-5.
Do note about the capital letters of the .EXE which is correct, i.e., the filename is case sensitive;
2. Just copy and paste the above "current" link and modify it for the version of the firmware that you wish to find, say:-
http://www.pentax.jp/english/support/digital/firmware/k5_e103w.EXE
3. That's it! I've checked that K-5 firmware files for versions 1.01, 1.03, 1.10, 1.11 and 1.12 are all there! (Except for 1.02)
Next, you might want to do the downgrade. I guess it is not allowed by the camera when it checks the firmware version of the .bin file, you may try this old method which was proven to work with older Pentax DSLRs. Anyway, I haven't tried it myself and you should do everything at your own risk if you follow and try!
Related:-
How to Get Back to an Older Version of the Firmware?