You can capture IMSI addresses from the GSM tower using an RTL-SDR key. How about storing captured IMSI's in database? This tool can help you to compare your captures and show which IMSI's you've seen before.

It requires gr-gsm installed and RTL-SDR connected

pip3 install scapy scipy numpy
python3 main.py

Used https://github.com/Oros42/IMSI-catcher Try it first!