eBay UK has everything you need for a classic British lightweight from the '50s, even as high-end as a Hetchins. I'm not sure why you'd be particularly adverse to it. Many of the best vendors there for such things are active members in the community and very knowledgeable.
In any case, most British bikes of the time were primarily equipped with British components, as there was a huge and competitive market. I would search for that stuff before delving into imported stuff from France and Italy, which was also influential but less common.
Campagnolo and Simplex gears are the main exceptions. Well regarded throughout the fifties with Cyclo-Benelux being the only really good British alternative.
Start at velobase.com and use the search function for whatever parts you're after, narrow the search to 1950s and made in England, and you'll get loads of results.
Head over to the classiclightweights.co.uk site to read about many of the period companies, technology, and to peruse lots of examples of built up bikes from the era in the "readers' bikes" section. And always keep asking questions when necessary!
Cheers!
-Gregory
Last edited by Kilroy1988; 02-23-21 at 06:32 PM.