Technically, JASC palettes are text files storing each color's RGB data on a separate line. You could hexedit an existing ra2 pal file, if you know how to...
Or, if you have an 8-bit PCX with that palette applied, you could use XCC Mixer to Copy it as PAL...
You could use PPM's JASC2C&C palette converter...
nice easy way is to apply the pallete to a PCX, then use XCC mixer, click on the image, then right click "Save as .PAL" not the (Jasc) version.
Sonovabitch. Here I am wondering why the 'save as PAL' option is always greyed out when another palette format is selected. It only works when a PCX is selected (!) *smacks head*.