The African snakes in private collections in Australia are all illegal so you'll probably struggle to find anyone willing to let you film them. Zoos will be more accommodating and much easier to find, but they'll be very strict about permits etc, unless you just want to take some happy snaps for your own personal photo album, in which case it's just a matter of throwing a few compliments at the right person, buying them lunch and asking nicely.
Until early last year it would have been much easier to just fly over to Asia and film some there. When I lived in Asia I had friends who would get (fully legal) imports from Africa and it was fun to be there while a hundred or so African snakes were unboxed. Flights to the USA are more expensive but African snakes are similarly easy to film there. Currently international travel is a complete clustercluck but still probably easier than legally filming African snakes in Australia. Of course, heading to Africa itself is an option.