Yes, your best bet is the Hardly Strictly Bluegrass Festival in San Francisco October 3-5. Steve will be appearing with the Bluegrass Dukes, and typically he is the last act on Saturday. If Allison is added to the bill, you can count on him joining her for a song or two. HSBF also has a songwriters circle, and Steve is usually a part of it.
Justin is also on the bill. Does Steve ever sit in with his son?
http://www.strictlybluegrass.com/
And it's 100% free (thank you, Warren).