So you want one professional outsider to drive the revenue of 100 different non-affiliated entities? That would at first seem ridiculous. The only people even tracking the growth of 100 unaffiliated companies are fund managers - not advisors. The only other groups with a vested interest in that many unaffiliated companies are industry associations.
But since we're spitballing lets assume that each of the 100 stated companies has an average of 12.5M in revenue and 50 employees (for a round number) - so you you're talking about a population of 5,000 people. And they are from unrelated companies so they don't share the same work culture or even leadership.
So basically you're talking about the nature of the human condition with a sample group of 5,000 people and wondering what drives human beings to be able to reach exponential growth (10-35% within 8.5 months assuming there are no hockey stick growth start-ups in there to blow the curve). And you're wondering what a consultant would "do" and what assurance you get. The answer is... nothing. This isn't a consulting issue. It's a training issue.
When you're talking about 5,000 people with roughly 50 different CEOs and or business owners the only way to even reach them is through training (online or in person). No single advisor can cover that much ground in that amount of time and a large consulting firm would just manage the situation through spreadsheets and quantitative research with some freshly minted MBA working with you (mobile phone in one hand and a fire extinguisher in the other) after a Partner in the firm sold you the goods .
So you represent an industry association and need corporate training that can help your members move margin - and quickly - in order that you can stay relevant to the membership, keep the dues coming in and the overhead paid and be able to fulfill the mission that the members have trusted you with as their industry representative. Got it.
Invest in the training of these companies but train only their executive leadership - as the head so goes the body. And invest in training in and around the realignment of belief, mindset and human achievement. And ensure that these senior executives get beyond "knowing" and get through to understanding so they can go back to their companies fundamentally changed in who they have been being in relationship to their own goals and can lead thusly, empowering their management teams to have the personal breakthroughs necessary to power their respective divisions through to breakthrough growth . Again - as the head goes - so goes the body.
Do this NOW and by the end of the year you'll have leading indicators to success but unless the economy miraculously spikes by 20% or more you more than likely won't have the growth you're looking for for your members. That growth will likely take another year of reinforcement of the stated training principles along with measured, accountable sales and marketing efforts that are driven from the mindset - so reset expectations. It would take a solid year past your target of the end of this year but it is do-able. Anything is possible. That's my belief.
Insofar as "assurance" no one can ensure or assure that they'll even wake up tomorrow morning (that's why insurance exists). Life is tenuous and subject to unannounced change - and people hate change, btw - which is why these things take time.
I hope that was helpful.