Thank you all for your recommendations.
I eventually went for mail order, as each nursery within an easy drive only stocked one of types of bare-root fruit tree in which I was interested.
Bauchery looked promising but their website was a little ambiguous regarding whether or not they could despatch all elements of the order in one go. I emailed them to ask, and they replied to say that they would complete the order in one lot - perfect. But when I went to order, 2 of my required plants were out of stock.
I then found Meilland et Richardier who seemed to have everything in stock for a similar price so I placed my order.
The site explained that all orders for bare root trees would involve selecting then digging up the required specimens before packing them and despatching.
The trees arrived 9 days after I placed my order, wrapped in plastic and inside a long card box. They all seemed to have a large and well-developed root system - length varied from 80cm (noisette) to 1.5m (apple - reine des reinetttes). The trees came with clear instructions, so I put the bare rooted trees into a wheelbarrow and covered the roots with wet earth for two days until I was ready to plant them.
Planting took place two weeks ago, and all 4 trees (apple, nectarine, pear, hazelnut) are showing signs of growth.
I’ll post an update in a few years when they have borne fruit