The Gospel Coalition Resource Library has nearly 400 sermons, lectures, and conference addresses on the book of Hebrews.
David deSilva, "Hebrews Bible Study 1st Session" Youtube 10mins.
David Pawson, "Hebrews," Unlocking the New Testament audio. David Pawson is one of the most renowned British expositor of the Bible. This link takes you to his 13 part course on Hebrews. 
The Book of Hebrews. 2 studies. video 57:43.
