Matchroom currently has four kinds of tournaments....
Invitationals, like the Mosconi Cup -- small group of invited players
Large Matchroom-produced opens -- like the US Open and the European Open that have a mix half seeded players and half unseeded. While it has been possible for anyone to enter these directly if you are quick, it seems that Matchroom will be looking to make the entries by non-tour-card players through qualifying events
Independent events that anyone can enter, such as DCC nine ball and the Jacoby Scottish Open.
The Matchroom schedule has just been updated to include a lot more events but it is not yet complete through the end of the year:
matchroompool.com