You could look into markets that are served by old monopolistic companies. If you for example could get a list of medium sized companies sorted descending by age, then some of them should be in monopolistic situations (more than 50% market share or so). Since they are so old, I doubt that they will be able to stay innovative. Then make a list of innovations during the last 5 years or so, which have been real game changers: bio technology, wireless communication, internet speed, ebooks etc. and consider whether any of these technologies could be a game changer also in their market.
If not, then make a list of recent fundamental social changes: Green movement, risk of terrorism, changed immigration, social media, piracy (somalia), news broadcasting (Twitter, internet newspapers), usage of communication media (SMS, Twitter), etc. and consider whether any of these social changes could change the game also in their market.
If not, then make a list recent large price changes for widely used products: increased raw material prices (copper, gold, rare earth minerals), food prices (grain), lighting prices (LED lamps), broadband prices, roaming phoning (in Europe), flight prices (low cost carriers like Easy Jet, Ryanair), cost of capital, home prices, robotics, cost of some types of chinese/indian low-cost labour, price changes due to changes in subsidies/taxation or opening/closing of markets. See if any of these changes also severely affect their market.
Chances are that an old monopolistic company will not be able to keep up with such fundemental changes, meaning that new markets/niches arise.