Prior to the Old republic giving Chancellor Palpatine the extraordinary powers that would lead to it becoming the empire, there were not great fleets of combat ships and weapons. At the time of Plagious the Republic had lived in peace for so long that there was not a great trade in weapons or need for Military grade weaponry. So yes at that time there were very few of these types of weapons available in the Republic.
With in few years of this incident the Empire would emerge and that demand and supply would grow exponentially.
It is also important to note that the word used was rare not that it was unheard of or even unpredictable that his enemies would use it. Just that the rarity and cost of such items helped Plagious to focus his investigation into the perpetrators on those people with the power and money to acquire them.