If you want higher Perception obstacles, start looking for things that are more difficult to notice—but which aren't covered by a skill! To pass these sorts of tests will probably require artha. Beginner's Luck is also an excellent way to earn those tests, so learn a Perception-rooted skill or any new wise.
It is the GM’s role to assign appropriate obstacles based on the inherent complexity of the task at hand. (BWG 14-15)
Perception is the awareness and mental acuity stat. It’s rolled all the time in game. Players always have their characters searching for information or clues, and this is the stat tested in those situations. (BWG 17)
Occasionally, a test has no fixed obstacle. It is simply a matter of testing an ability and noting how many successes are generated. This is often the case for research, searching an area or other knowledge-based skills. The amount of information distributed by the GM is directly dependent on the number of successes generated. (BWG 26)
Let's say the player wants to search the room. That's a Task, but let's establish Intent (BWG 24).
They have no idea what they're looking for, so they say they're looking for clues or whatever. Perfect use of a graduated test. The GM provides information based on however many successes are rolled. The player would log a Ob 1 test toward advancement of Perception if they passed, but unless their Perception is 1 (or, due to wound penalties, reduced to 1), this is a routine test and thus useless for advancing a stat.
They want to find the key to the chamberlain's room. Does that Intent make sense? Is it possible the key would be here? If so, GM specifies an Obstacle per the table on page 15. The player logs the appropriate test given the Ob.
They want to find a particular person in a crowded room. See the Observation skill—this is not a Perception test! This is a versus test between the observer player (possibly a Beginner's Luck Observation test) and whoever's hiding and how they're hiding, probably Inconspicuous.