Step 1 is definitely to talk with your client and discuss what manual steps they are doing to find these leads, and try to automate or use AI to shorten time to find the leads.
Some random thoughts as signals:
Scrape some of these sites
Acquire.com (fka MicroAcquire), BizBuySell, Empire Flippers, FE International, Flippa (online), Axial (mid-market), DealStream, etc.
Look if they hired a CEO or CFO recently
Look for companies that fired x% of their team in clay
decrease number of employees, especially sales compared to last 6 months
etc, play around with this.
hope this helps Adam A.