"footage of Hennessy's pub"
I doubt if any exists; would be interested to see it if it did.
Hennessy's (now long closed sadly) was a small bar not ideally shaped for sessions, let alone filming them. Whenever Johnny was there the place was heaving full.
After Hennesey's closed Johnny frequented The Westbridge on the main street.
I have a sneaking feeling that TG4 made a television programme about him following his death, but am not sure of this.
You might try contacting Oidreach an Chlair (OAC), the local heritage organisation, via their website, they should be able to tell you what there is.
Jim Carroll