All the devices are stored in the librenms datebase devices table.

You can dump all of them with the following command from a shell prompt.

sudo mysql -u librenms  -p librenms -e "select hostname,sysName from devices"

Example output

[jim@localhost ~]$ sudo mysql -p librenms -e "select hostname,sysName from devices"
 Enter password:
 +----------------------------------------+--------------------------------+
 | hostname                               | sysName                        |
 +----------------------------------------+--------------------------------+
 | 192.168.1.1                            | linksys                        |
 | 192.168.1.9                            | wifi-unifi                     |
 +----------------------------------------+--------------------------------+