It is relatively easy to find American computer artifacts from the 50s to the 80s.
Are you... uhm... this might sound silly but... checking Britain? ebay.co.uk will probably have a wee bit more.
You see Acorns, Dragons and BBC micro's on and off... but sadly their production numbers never really amounted to much compared to the American market. Like anything else where the production numbers are lower it gets harder to find them.
See trying to find a zed-ex 80 or even 81, compared to the mass produced Timex Sinclair 1000 that by the mid 80's you could by for $30 at the local pharmacy. (ALWAYS found it odd that they started selling them through CVS and Walgreens). You see them from time to time, but you can ALWAYS find multiple TS1K.
... and let's face it, prior to 1980 the production numbers for the UK make Apple's sales prior to that time look good; when up until the early 80's Apple held a solid last place in the US market. For all the revisionist history they've managed to manufacture prior to 1982, Apple was outsold 10:1 by Atari and 25:1 by TRS-80; then Commodore in two machines (VIC and C64) outsold an entire decade of the Apple II in just two years.
Simple fact is if there weren't a lot of them to begin with, good luck finding them now -- though that lack of supply also makes the handful in circulation worth more, and more likely to be held onto by the people who do have them keeping them out of circulation.
See the IBM PC, where they made SO many of them and mechanically they are so over-engineered that to be brutally frank a stock perfect condition one shouldn't go for more than $150 with the monitor.They're not worth as much as there's so many of them.
Hence why most anything that says "collectors edition" on it is worthless trash; see the woz "signed" IIGS. They slap the name on it to trick people into spending a few dollars more on it, churn 'em out like hotcakes and the end result is everyone who wants one has one, and the market is flooded meaning they'll never be worth anything.
You see this in toys, comics and sports cards ALL the time! Action Comics #1 is worth a fortune as it was a small print run of something many people ended up using to wipe on the bog so few examples even survived to today; the "Limited Collectors' Edition" copy of Superman:The Movie from '79? Worthless. An original year Barbie NiB? Big bucks; that Beauty and the Beast "collectors edition" Belle? Pretty much worth half the sticker price it was when new.