So, we are talking about the new FN pistol that fires the same ammo the P-90 does?
I am not totally sure the ammo out there right now is really ammo piercing. I don't THINK it is, as a matter of fact.
None of the stuff that was actually intended to be armor piercing has ever been sold to civilians in the US. There were some defective hollowpoint rounds that actually got out to civilian sales that will penetrate IIA vests (cavity too small, jacket material too strong) but that was only a few cases worth and it was recalled/withdrawn as soon as someone found out. The standard ammo for sale in 5.7 is a hollowpoint that won't penetrate soft body armor (unless you're stupid enough to order and wear level I armor).
You are correct:
While there is "armor piercing" ammo for the Five seveN, it's not available in this country, not to commoners, anyway.
OTOH, just about any non-hollow-point round from a .44 mag will defeat any body armor you can carry around...