Go to www.abebooks.com and search for Wal Winfer.

I got 23 hits.

Winfer books focus on the British Single shot. One Seller is offering all five the currently available volumes.

While you are there you can also use the advanced search function and query "single shot rifles" in quotes and as three words. I got 126 hits there. A lot of De Haas and Grant.

Jon Kirton got me two hits.

You can also search for specific rifles in the keyword search.