[WillPS]

Challenge haven't showed any Holness era Blockbusters in years unfortunately. The Simon Mayo series appears occasionally as schedule filler (presumably this is more readily available to them whenever since they commissioned it). When they did show it they showed the first few dozen episodes of the first series (1983) and a few dozen episodes of the final ITV network series (1992), as well as the reprised series originally comissioned for Sky One (1994). These episodes are all/mostly on YouTube (unoffically), along with some captures from original screenings or 90s repeats.

The rights belong to ITV but it's not being streamed anywhere officially. Even if they were it's worth remembering that they were making hundreds of episodes a year so it'd be a bit of a needle in a haystack unless you happen to know the specific series and episode.

Sorry to be the bearer of bad news.