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I jointly run Paradise Cycles in Bethnal Green. If we are not in your neck of the woods I would maybe recommend going to shops that are more workshops than bike retail spaces, they tend to be more understanding of the needs of a cyclist/home mechanic as I think someone said above.
It is tricky stocking everything within a rented London premise, you just need to find a shop where the employees think about bikes like you, and therefore value using their space for the things that you want, rather than retailing as many Pinnacles as possible!
Well I'm sure some still exist, I was talking generally... [edit: and describing a tendency, pointed out by others above. I understand businesses need to survive, but if it means some no longer sell basic stuff for -mostly- self sufficient cyclists who are not in the market for a Taiwanese made bike, then I have to, and had to, buy what I need online; the shops I have access to geographically without making an expedition out of it have not given me much of a choice]
To be fair one of my local sorted me out for basic stuff a few times, but they are quite limited. I bought a sealed bottom bracket and the only choice was Sunrace and Oxford depending on axle length... Why not stock basic Shimano UN55 or whatever the reference is? I'm happy to pay more than online if I can cycle down the road and get it right away.
Where's your shop so I know for the future... :)