How can security leaders in smaller organizations stay informed about emerging threats if they don’t have access to formal threat intelligence feeds?

CISA, BleepingComputer.com, Dark Reading, Krebs on Security, join a low-cost information sharing organization specific to your industry.

Like others have mentioned, smaller organizations can stay informed by leveraging free community threat-intelligence sources, industry forums, and information-sharing groups. With the help of AI platforms and well-crafted prompts, it’s also possible to quickly access the latest insights on the threat landscape.

US-CERT / CISA Alerts – free, high-quality advisories on active threats and vulnerabilities
SANS Internet Storm Center (ISC) – daily threat diaries, honeypot data, and analysis
Public forums such as Reddit communities (r/netsec, r/cybersecurity, r/blueteamsec) that offer active discussions on emerging threats"

As others have mentioned - reports from CISA (or your local equivalent) are free and useful. Join an industry forum so that you can share information and observations.

Have a Threat Profile prepared for your organisation and updated periodically.

I also want to point out, don't lose sight of the fundamentals. Inventories, Patching (particularly the edge) and hardening, Monitoring, ability to Respond & Recover. The majority of cyber threats are still hindered by getting the basics covered.

Most strategic threat intelligence relevant to planning is published for free by most threat intelligence shops, you don't need feeds for this. You might want to ask someone to compile you relevant things once a quartner/annually.

One way is to subscribe to some of newsfeed such as:
https://www.infosecurity-magazine.com/
https://www.bleepingcomputer.com/
https://www.cisa.gov/news-events/cybersecurity-advisories

Microsoft has good blog site as well at https://www.microsoft.com/en-us/security/blog/ which has a section on Threat Intelligence and Security Insider.

Attend Black Hat conference if possible. Hope this helps.