have an eye to/for the main chance
have an eye on/for/to the main chance
To be continuously seeking opportunities to advance oneself or make money. The term often refers to someone who is ambitious without consideration of others. Primarily heard in UK, Australia. You just have an eye on the main chance—you don't care if I succeed or fail.
have (or with) an eye for (or on or to) the main chancelook or be looking for an opportunity to take advantage of a situation for personal gain, especially when this is financial.
This expression is taken from the use of main chance in the gambling game of hazard, where it refers to a number (5, 6, 7, or 8) called by a player before throwing the dice.