Given the variation in the letters (look at the cover closely), I suspect this was hand lettered in the gothic/medieval style.

Locksley, by Scriptorium, is similar.

It also resembles a 19th century face called Oxonian in a type specimen by the British foundry Michaelmas 1883, but again not a spot-on match. A modern version.

Try a google search for Gothic Initials, there are many and they vary considerably, but you may come across something close that you can adapt or something to enjoy as an alternative.