Add Igniter'n'things vendor to Security. Or just straight up more Securitrons.

[The Grim Sleeper]

there's a vendomat in the same room as your lockers which produces those things which is presumably where you get the rest of the securitron components

According to the maps, that's only on Cog1. (and yes, I did not even notice that one, so thank you).

I think securitrons also need a robot arm to work.

You are correct. And if at all possible, a supply of them in the office would also be much appreciated.
Or just straight up securitrons.