Selling Physical Copies
To have physical copies of books on shelves, try approaching local book shops, or shops that stock products similar to the genre of your book. Most bookshops are only just starting to reopen, so maybe chatting to them to find a mutual connection, like maybe arranging a signing session which will benefit both you and the bookshop, could be a good move. Please stay savvy if you leave books with them without payment. Maybe find a simple 'sale or return' contract online that you can print off.
For Waterstones, contact the branch manager of your local store. Beware though, as some insist on high royalties.
For WHSmith, their head office has the following instructions.
"Please send a sample of your book for the attention of either Head of Fiction, Senior Buyer Non Fiction or Head of Childrens' Books to:
Delivery Point B
Due to the volume of requests we receive, we will contact you only if we are interested in stocking your book, and we are also unable to guarantee the return of your book.
If you have written about places of local interest or local history, and your book is not a children's book, you may approach the Manager of your local store. They may agree to sell your book however they are not obliged to. Their decision will largely depend on their local book budget and whether they believe the title will sell. All local titles are bought on a sale or return basis."