Services will include communication structure audits, agency search and selection for M&A and benchmarking studies.
In June, Gornall left Consolidated Communications - the agency he founded in 1990 - when he sold the agency to its management.
'We aim to help and empower management directors to capitalise on their PR agencies and improve power and value by building and selling,' said Gornall.
'Many agencies require outside experts to advise them on mergers and acquisitions and other business matters.
'There is a lot of PR M&A activity presently and we can help agencies look at their in-house situation and decide if one plus one equals three,' he added.
MGA, which launched last week, is already overseeing some unannounced takeovers and mergers, revealed Gornall.
Ashe recently left his chief executive post at City PR firm GCI Financial.
In the 1990s, he founded City PR firm Focus Communications, which he sold to GCI UK in 1998. He was also previously head of the global financial practice within the GCI Group.
Prior to MGA, Madsen set up Madsen Clark, an M&A consultancy specialising in the PR industry.
Its search and selection team introduced a number of transactions, including QBO and Harvard PR to Chime Communications, and Propeller Direction and Lexington Communications to Lexis PR.
MGA will serve all areas of the marketing community, said Ashe.
The consultancy will 'facilitate PR agencies with corporate developments through M&A advice and provide a range of consultancy services'.
MGA also plans to provide CEO mentoring, market research, strategy development and profit improvement.
'We are developing a register of approved suppliers for follow-on work in areas such as training and development, search and selection, IT, property advice and database marketing,' said Ashe.