There are some videos still available on YouTube but I could only find a short clip of GWD as Arthur singing at the end of:
"If Ever I Would Leave You" is one of Lancelot's songs.
Many of us would like a video of Camelot but we've heard nothing about one.
Most modern plays (written after the Berne Convention of 1886) are protected and have royalties/fees that must be paid to the play owners. The contracts are very specific as to how the production can be used, i.e., staged only, staged and filmed for TV, staged and filmed for sale, etc. They may include a time frame as well. i.e., the right to perform ends after a set number of performances or a specific date. The more "flexible" the contract is, the more expensive it becomes.
Classic plays such as Shakespeare are public domain and have no royalties. The staging and costuming may be copyrighted by a producer or backer which is why most companies do their own staging.