I recently picked up a U.S. Marine Corps Tech. Manual for a M1014. It does not give any hints as to a spare parts list. From what I have read on this site, I have not picked up any info that would help either.
As for a telescoping/collapsible stock, your M1014 needs a a recoil spring tube with proper detents(047J), a pistol grip handle assembly (117J), and a telescoping stock assembly (265J). If I understand correctly and you have a pistol grip assembly (160J) on your gun. That is what you will need.
The owners here in the US of M1014's, item number 11701, have not been able to obtain the recoil spring tube to allow us to have our gun do what Benelli is now selling to the public in a M1014 item number 11707 configuration.
I advise you to get the parts there. In fact would do me a favor, would you please PM me about you getting me the parts that I need for my gun.
PLEASE HELP!