It's the independent Garden Centres, which are worth while supporting as they are more prepared to order in more unusual plants, there is a pretty good chance that the man or woman you are talking to will be putting in the orders with the nurserys or will be talking directly with the one who does.
mostly orders go in at the beginning of the week for delivery thursday or friday.
Seed ranges are standardised a company like suttons will send a range of around a 100 or 200 seeds depending on the footage to a GC once or maybe twice a year. (unsold go back for credit). If you want anything outside of these ranges online is the way to go. Garden furniture tends to be sourced from china either direct by chains like b&q or via wholesalers who pretty much charge the GC at around the price a chain sells at retail.
Things like sheds, fencing, dog boxes and unusual handcrafted items can be locally produced and custom made which supports the local economy. Most independent gardencentres will produce individual planters and hanging baskets to order, you can often get last years refilled. Of course if you are a regular customer at an independent you are more likely to be able to get things sourced for you,(if it is the right time of year).
Last year in my area at least 4 independents went bust. It's pretty tight for the rest of them too. Have a day out , enjoy a cream tea, find plants you like and if you don't see what you are looking for ask.
You might find your local independent agreeable to a little bit of haggling on the price of plants. This is where it helps to be a regular customer but please don't do this when you just want a couple of bedding plants, if your spending cash (not cards as visa are already taking a chunk out of the profit margin) and buying a good number of plants thats when your more likely to get a deal particularly on the quieter wetter colder days.