Clevedon Steam, steam plants, steam fittings etc.
Macclesfield Model Engineering Supplies, brass copper and aluminium sheets, bar stock etc. BA screws and nuts small hand tools taps and dies.
Deluxe Materials, adhesives.
Cornwall Model Boats, everything from kits to rigging thread.
Deans Marine, specialise in 1/96 scale warships and fittings.
Component Shop, batteries, wiring, connectors and Action speed controller😎s (made in UK)
Mtronics speed controllers, made in Batley, Yorkshire.
I could go on, we in the UK are blessed (compared to some other countries) with the choice available...

Ditto LewZ and thadlietz,
My supplies, parts, glues, almost exclusively come from on-line. LHS have for a long while complained that on-line sales hurt them, but at the same time, they do not stock very much to begin with. It has become a self fulfilling prophesy. Sadly.
We have two LHS in the entire State and neither caters to boats except RTR. I have lost my inclination to drive 2-3 hours to a LHS only to find that they do not stock what I need.
I am very jealous of everyone across the Pond. You have gold mines. Don't let them fail.

I concur with LewZ, here on the left coast I find the same thing. Amazon and Ebay are somewhat helpful but most hobby shops here just don't cater to the scale boating scene. There is one shop here in Sacramento that does better but for the most part I resort to ordering from the UK. Although I was able to pick up a new in box 10th Anniversary Model Slipways Vliestroom kit with extras! Pristine condition at the Sacramento Shop so there's hope.
Cheers😁

USA:

Unfortunately, I can't recommend anyone here that gives great service to the model boat builder.

Locally (within a decent driving radius) in this area all the hobby shops, the few there are, don't support the scale model boat builder. Some "shops" can help with r/c and motors, batteries, plastic shapes, some hobby wood, etc., but they know very little about scale boats. R/c speed boats, cars, planes, OK.

Nation wide, unless one is looking at RTR (ugh), can probably count them on one hand. Those are usually mail/internet ordering businesses that are focused on supplying items, and not that much help in solving problems.

I get emails from people wanting repair or rebuilding work done but I have enough of my own work to do.

This is where clubs and forums like this comes in quite handy.

Lew
Florida ⛱️, USA ❤️