Anyone who lacks a license can drop the offending items off with the guards, wherein they'll be held in a closed-off, very secured area for them to retrieve outside of the walls. Those who require a license should be cleared by at least two to three First Squad members, each being able to vouch for that person's trustworthiness, morals and sanity, if need be.
Due to this, anyone seeking to sell explosives should do so outside of Cellsvich, for if someone is found selling explosives to someone without a license with the city, especially after they've been directly notified of this measure, they will be punished accordingly.
Additionally, the guards at the Gate have been notified to search anyone coming in (or out, if they have good reason to do so) for any explosives they might be carrying, hidden or otherwise. The Mage's Guild has also been informed of this, and a set of guards will stand by to perform the same searches on those going through the Majistra portals. For future reference, this will also apply to any other notable entrance to Cellsvich.