It seems, Captain Wentworth isn’t as interesting as Darcy by far. Still, I managed to find a few books, plus a few of others featuring other heroes of Austen.

Amanda Grange:

• Captain Wentworth’s Diary
• Mr. Knightley’s Diary
• Edmund Bertram’s Diary
• Colonel Brandon’s Diary

Susan Kaye:

• None But You (Frederick Wentworth, captain: book 1)
• For You Alone (Frederick Wentworth, Captain: book 2)

Rachel Billington:

• Emma & Knightley: Perfect Happiness in Highbury