Day One have weighed in with another in the 'Travel with...' Series. Rather confusingly they have another of a similar name for children in their large format 'Footsteps of the Past' Series. For devotees there is a '365 Days with...', and most recently, a new study by John Pollock - 'Abolition!'
Kingsway have republished the classic Pollock biography 'Wilberforce'.
Christian Focus have had 'William Wilberforce - Vital Christianity' by Murray Pura out for some time. They have also added 'The Freedom Fighter' by Derick Bingham to their 'Trailblazers' Series for children, as well as an interesting book on the slave trade itself called 'Voices Against Slavery' also aimed at young people.
One other book - only just out in time from Crossway - is 'Amazing Grace in the Life of William Wilberforce' by John Piper. This follows a theme not lost on other writers, of the relationship between old John Newton and Wilberforce, especially in the way that Newton encouraged him to believe that just because he had been converted didn't mean that Wilberforce should think that his career in politics was over.
You really are spoilt for choice now!