I dont think the HK PDW will be available to civilians, due to the effecientcy of the ammo at going through armor. I would love to get one, but only in 9mm or .45 ACP, as shooting the special ammo would be too expensive.
I can find no reference to an FN PDW, maybe you mean the P90? Acording to the FN sight: "Law Enforcement agencies only- 5.7 x 28 caliber weapons are not available to the general public" so, your out of luck with them too. They are $1350, though.
Whoever said the pen is mightier than the sword obviously never encountered automatic weapons.