The best place to start would be call up the potential manufacturers and ask them if they look at new technologies or inventions for potential licensing. Some long standing industries with very few players are very difficult industries to licence in.

If actually pitching the technology, you should have IP and I recommend filing a provisional patent which gives a year of patent pending status. Also if you qualify as a micro entity, the PPA filing fee is only $65.

This allows you to pitch to companies with a provisional patent and find out the level of interest prior to investing in the much more costly non provisional patent.

Check out https://www.balancedpayments.com/
They are made for marketplaces.

Airbnb CEO among others invested in them and they have some of the best pricing/payout fees.

Also some good info on http://www.collaborativeconsumption.com/2013/10/08/online-marketplaces-are-hard/
One of Balanced Payments co-founders is writing this blog series on marketplaces.

Correction to Airbnb example: (it is 3% to the host and between 6 and 12% to the renter.
If the 'supply side' gets 100% payment, there is no incentive for 'supply' to encourage going around the service especially since they receive benefits of secured bookings and payments.

With freemium like Craigslist and Kijiji there are some advantages with a large number of users. However, the quality of supply (bare bones listings), responses (people not responding or not meeting when they say they will) can easily be over 50% which hurts customer experience.