Walsh Trott Chick Smith and the PR consultancy The Media Foundry are among the agencies Simons is talking to. The list is also thought to include branding, research and design agencies.
A date has not yet been set for the flotation, although the plans are well under way, according to sources.
The creation of a marketing services group would allow the agencies to pitch for integrated business as well as pass on leads from existing clients.
Last year, Campaign uncovered discussions by Long-Acre Partners about creating a best-of-breed holding company to rival the big networks on pitches. Such conglomerations give agencies enough financial scale to float.
Simons' plans are being firmed up as holding companies are busy snapping up the few remaining independent agencies. This year, Chime has bought VCCP, Delaney Lund Knox Warren & Partners has joined Creston and Cossette has bought Miles Calcraft Briginshaw Duffy.
Walsh Trott, DFGW, Mother, Clemmow Hornby Inge and WCRS, which has bought its independence from Havas, all remain independent.
Simons said: "We are looking at the possibility of creating a new entity. It is too early to say when it will happen."