While I would normally consider something from the edges of the empire unlikely to be representative of typical Achaemenid material, it's been suggested that this dagger from Medgidia is an artefact from Darius the Great's invasion of Scythia, specifically a battle with the Getae. I don't entirely know what to make of it.
Unfortunately, it didn't come from a controlled dig, so its exact age and origins are less likely to be determined. If it is Medo-Persian, it exhibits some unusual features. The scabbard has no chape (granted, this may have fallen off) or guard-enveloping throat; these features put it more in line with examples other than Medo-Persian ones. The general style of the hilt is common to multiple countries, including Iran. I'm not familiar enough with the decoration to know whether it would help indicate origins.
It may be Scythian, given Thrace's proximity to Scythia, or it may even be of native Thracian manufacture, but if it was actually brought from the core Achaemenid territories by Darius' army, it may be precedent for a less rigid image of what reenactors ought to be carrying.
