Here are some adverts the company placed in trade journals featuring DMUs:
This early advert featuring 56114 came in two versions for full page and half page use.
The first of the colour adverts below, which was in use by January 1958, mentions they had orders for over 250 vehicles, on the second which appeared by April 1959 mentions 400 vehicles. Note how the title describes them as 'Craven' rather than 'Cravens' DMUs.
A thread on the Sheffield History forum has some other (non-DMU) company adverts, as well as some other company details.
Additional adverts can be found on the Railway Adverts website.