I've worked on Leadership Assessment & Dev't projects for about 10 years and if i were looking at your CV I would be looking for evidence of a few key areas:
- Examples of how you have guided/coached others to alter their behaviour in some way
- The link between your efforts to influence others and tangible business results
- Your knowledge and understanding of the theories of leadership and their application to business
- Your own leadership experience
- Your knowledge of the leadership challenges faced by individuals at certain levels in various industries
I imagine you'd have some of the theoretical knowledge from your MBA, but there is alot out there.
One route in might be to play your HR card and opt for a stepping stone role? I.e. generalist to specialist. Bear in mind however that not all firms believe leadership development has anything to do with HR :)
Firms you might like to consider are CHPD, Cedar, Crelos.