Hi,
if the have SSH enabled, you can find the with their ssh server string.
user@server:~$ nmap -A -T4 -p 22 -n 192.168.0.1
Starting Nmap 6.40 ( http://nmap.org ) at 2015-07-27 22:12 CEST
Nmap scan report for 192.168.0.1
Host is up (0.00034s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh MikroTik RouterOS sshd (protocol 2.0)
|_ssh-hostkey: 1024 de:ad:be:ef:de:ad:be:ef:de:ad:be:ef:de:ad:be (DSA)
Service Info: OS: Linux; Device: router; CPE: cpe:/o:linux:linux_kernel
Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 0.65 seconds
Some bash script wrapping this should be able to find all your MikroTiks.
Another way that comes to my mind is listenig for the MNDP packets (
http://wiki.mikrotik.com/wiki/Manual:IP ... _discovery).
Ape