I found the InfraRed codes that the SA-AK25 remote uses: http://lirc.sourceforge.net/remotes/panasonic/SA-AK25
If your computer has an IR port on it you could use LIRC or WinLIRC. It's not exactly 'remote' control unless you have a laptop with IR.
Otherwise, universal remotes that have stereo libraries built in are around $100. You could get a cool touch screen universal remote for about $250. Stereo only replacements aren't very popular your best bet is one for your entire home theatre. Another alternative: You could pay a crack head $20 to go into radio shack and rip one off from the display stand, or save the $20 and do it yourself.