To date 6 Prowler units have been created by the DDS and the new special forces units have proved their worth on several black ops already (which of course can't be spoken about but you can read the stories). The DDS have decided to fund 6 more units and will look to expanding the fleet of special forces transports.
Currently there are 3 Fulcrums and 4 Corils dedicated to Prowler operations, more ships will be needed when the new units come on-line over the next couple of years. A 4th Fulcrum is understood to have been purchased from a third-party (the Fulcrum is a Utrek ship) though this has not been officially announced.