They`re not there. When the DVD was being processed, it was planned to include them, but after the 3 audio commentaries were added, there just wasn`t anymore room. But by then, it was too late to change the packaging. There is an easter egg tho, go to the bonus features page, and highlight the words at the top of the screen.
This actually made a few DVD mags a bit red faced, as they`d already `reviewed` the disc, adding that the casting tapes were on there. After the mistake was discovered, they had to apologise to their readers, as they`d reviewed the R1 versions, but said they were R2. Truth in journalism?.