"The Questor Tapes" is not currently available commercially on video. The only authorized video that I know of was a PAL format video from Great Britain, but it is long out of print. Every once in a while you can find someone selling a converted to NTSC copy of that tape on eBay and more recently on DVD-R. I have not purchased the DVD, but the copy I purchased on VHS from eBay a few years ago is of very good quality, so I expect at least that from the DVD. I do not sell nor make copies of this show as I am hoping Universal will release it soon.
UPDATE: I have found a seller while searching with Google. I won't be posting a link to the site, but you can search for "HARD TO FIND FILMS" and "QUESTOR TAPES" in Google to get to the site. I have not bought from this seller, but they do say that their copy is a "very nice quality print."