Congrats on what you have achieved with a change in the business last year. The Bush Boardroom sounds really cool and would love to host something there myself.
My suggestion would be to most certainly start a separate marketing channel (eg social media) for something like this. When talking to different audiences it pays to do this. You can then plug all the benefits of what this specific offering is all about. This doesn’t discount from cross promotion but it would be worth calling this out as a separate brand. Case studies (as you probably know) are very powerful and for something like this word of mouth works really well. Target audiences are hard as it will differ from business to business. Maybe even approaching a organisation like ‘Appoint Better Boards’ or something along those lines which have links into various Boards/organisations could be an angle. LinkedIn will be extremely helpful as well.
Good luck and happy to help if you require any more info.