The latest evidence is from an internal memo obtained by the anti-Hamas Palestine Press Agency that apparently shows a Hamas police directive to find rocket launchers and stop all rocket attacks against Israel, saying it is a severe violation of the law:
One interesting incident mentioned in that same report occurred last month, when a test rocket was fired out to sea on February 8th. It is unclear if that was Hamas or another group. But it is possible that they were testing out a newer Grad rocket, as the rocket that hit Beersheba might have been a new rocket that was manufactured in China.
Is it plausible that the smaller Salafist groups or Islamic Jihad are importing longer-range Grads? Even if so, Hamas is certainly aware of it.