You should review your concepts of ARP and Layer 2 switching. I will explain very briefly:
1- An ARP table is mapping between a MAC address and an IP address. You need an ARP table when you want to send/route an IP packet (Layer 3) to some host. Basically it means: if you send/route an IP packet to IP X please use MAC Y. An ARP table exists on hosts (PCs) and routers.
2- A MAC table is a mapping between a MAC address and a port on a switch. Basically it means: if you want to switch (i.e. Layer 2) a frame destinated to MAC X please forward through port Y. A MAC table exists on a switch.
As you see these are two highly distinct concepts.
On Junos, the following commands can be used:
1- to check the ARP table: show arp
2- to check the MAC table: show ethernet-switching table or show bridge mac-table (it depends of the platform, you haven't said which SRX you are using)
Is your SRX being used as a switch (transparent mode)? It seems not, so forget the MAC table.
In both cases you learn the mappings by listening to the traffic. If some device never sends traffic then your platform has no way to guess its MAC address whether it is for the ARP table or for the MAC table.
So the solution for your problem is to ping IP addresses one by one (or ping broadcast IP addresses of your LANs) and see the result with show arp