Short answer - search google for "top consulting firms".
Personally, I use LinkedIn a LOT for tracking people down. It would be easy enough to find the people who work for the large consulting firms (McKinsey, Bain, etc.) by searching by company name (and location specific too, if you want it). Another way is to join LinkedIn groups that are specific to your niche market, and search the members for the word consultant/advisor/etc. I also found a lot of consultants who were already LinkedIn connections of my target leads. They appeared as common links on so many of my targets, that I quickly got to know who the people to talk to were.
Old fashioned ways are at trade events, preferably ones that are more niche are the ones to go to. For example, if there are Expo's you can attend (i.e. free to walk-in) then hit up as many as you can, and you will start to recognize faces. Do the old meet and greet, don't be shy to talk to anybody, drop them a business card, chat for 3 minutes, and get to know them. This is a good way to meet new leads too.
Coming back to consultants, at the end of the day, our SaaS tool does in a few minutes, what they normally charge clients 100's of dollars per hour to do, and what they studied long nights at top universities, or worked tough jobs for a couple of decades, in order to position themselves where they are now. They don't like our tool, much the same way lawyers aren't going to like automated legal platforms, doctors aren't going to like auto-diagnosis machines, taxi drivers don't like uber, etc.
Consultants in the B2B environment are soon to be relics, in my opinion, unless they are ivy-league students with good connections at top firms (which is also super common in the consulting industry). Hence I mentioned about being the new kid on the block above.
I say cut out the middle man, spend the time wisely, and allocate the revenue that you WOULD HAVE had to share with them to a good marketing campaign.
Or make sure to be firm in your charging model: they're going to want special pricing, don't let them have it. And make sure there is a tiered-pricing mechanism in place (i.e. they more they use your platform, the more they pay) because in the end they might have a broader reach than you and start to target companies that you are already going after. Whatever the case, draw up the inter-company revenue sharing T&C's in advance, and think about the long term.