There are some runs of 5mm. rimfire ammo being made infrequently. CheaperThanDirt's new catalog has some.
However the 5.7 is the new with it fad round. Or has been for some time.
For the last 3 decades the military was going to go to sub-caliber weapons of 4mm.-5mm. Some were bullets and the rest were fletchette shooters. All the worlds militaries climbed on the subcaliber bandwagon and were going to field even fletchette firing rifles. One subcaliber fletchette at a time. Some of these were full auto.
The flawed thinking was that wounding was more human (gotta love the liberals.. it was there idea), cost the enemy man power and time dealing with casualties, and the battlefield less bloody.
All the brutal brushfire wars across the globe have proven this line of thinking false at every level.
When first introduced it was supposed to be for FN's P90. It's supposed to take place of a rifle and be issued to secondary or support troops. The reasoning(not sound by any means) was that something small and portable was needed by the non-combat frontline troops.
These also gave the ability to pierce then said bullet resistant vests from other countries militaries. That was back a few years and not truthful of present. At least this was possible with the round the military only,was able to get.
Problem is the submachine guns can or used to fill that roll. M4 carbines or such have taken the subguns place.
Documentation has shown that the special types of armor piercing 9x19 ammo would go through even class 2 ( pistol level protection) or 3 (rifle level protection) vests a decade or so ago.
There have been many documented cases of support troops getting into brutal firefights from Panama to recent and present history in Iraq.
The superior ballistic properties of the 5.6mm and larger rifle calibers(even in carbine guise) show that the short range 5.7mm. just isn't up to the job. Wounding ability falls off drastically at longer ranges. Not all engagements are close range affairs.
Given is the fact that the military armor piercing ammo is not for sale to us civilians.
Actual shootings ,few that they are, and media testing put the 5.7mm in the .22 magnum wounding ballpark. Granted I wouldn't want ot be shot with any firearm round, but that's a low level of internal ballistic abilities.
Casless ammo was also going to be the new wave thing also.
The world's militaries gave it all up after billions of dollars have been spent on all this and the idea has been dropped for the time being. Caseless ammo and the subcaliber guns rarely worked.
When your enemies are fanatical,give no quarter, will not surrender themselves, and will kill you and your fellow soldiers at any cost, leaving them still able to do so is not a good idea.
The FN product is know being marketed for civilians as a semiauto version.
Ammo for the most part has seen velocities reduced or the ammo's wounding abilites stifled.
A revolver either in 5mm. rimfire or one in 5.7mm centerfire does make sense considering the reduced ballistics out of the shortend handgun barrels.
As already stated the 5mm. ammo is rare if even seen.
The .17 rimfire calibers and .22rimfire rounds all are on the market already.
There seems little or no market for the either 5mm.at this time.
FN has buyers in the USA buying the 5.7mm carbines and pistols. It's more for a novelty than a real world need.