Is it harder for junior leaders to seek out a potential mentor or is it harder for senior leaders to find a mentee?

Neither is hard! Your got to want it! Mentors are people you admire and want to emulate. Some of my mentors don't even know who I am, but have had a profound influence in my life! I have been a mentor to many as well. I say, gravitate to those you admire, but always be true to who you are. The rest is just sausage making (the stuff nobody really talks about, but makes a hell of a sandwich)!

From my foxhole, I think it's harder for juniors to find and select the right mentor, as we all need them throughout our career. I believe the officer corps does this a bit better then the enlisted corps, but only a few have figured out this art .
I'm currently in the market for one, as the people around me are so overwhelmed with their day to day, that they randomly want to take on the senior NCO.
I do have people I can engage from retired "star level" CSMs to a few COLs, but typically these wells aren't as deep as needed sometime or their time is limited. As it's typically reviewing NCOERs, ERB, and more official papers affiliated with my record jacket.
This however doesn't meet what I consider a mentor to be.
So you have to define the level of mentorship first that one is requesting.
I think it's someone that can listen and help establish your short term and long term objectives and add input and how-to. Someone that can inject ideas on programs and rules that will help or hinder your ability to accomplish those goals. It's someone that can think, not just about the job or perhaps things affiliated with the job, but remember that your a person and should be viewed like that. Lastly, someone that can understand your experiences and the level of "rat race" your in. Someone that can speak to it, as not always from experience or judgment, but just by thinking and relating.

The senior NCO should mentor everyone in his charge. A junior leader is still trying to find themselves let alone pick a mentor. We as leaders should lead by example and make it to where all junior personnel want you to be their mentor and follow your example.

Honestly, I think its difficult at times for Jr's to find someone to mentor them. I mean, if a Sr. leader wanted to find a Jr., all they would have to do is walk down to the motor-pool on whatever day said leaders maintenance day is ( I.E.: Motorpool Monday's) and throw a rock in any direction. Listen for the Ouch!, And Vola! You have found someone to mentor. All jokes aside, i think the rapprochement process is the most difficult. From day one Joe is taught to steer clear of anything that has shiny on its chest, and anything with more than 3 stripes will just make you push.

I look at it like this: as an individual it is your responsibility to seek mentorship in those more experienced than yourself. And likewise, if you have applicable experiences or knowledge then it is your responsibility to pass that knowledge to your Soldiers. I don't think it has much to do with subordinates or superiors becuase as a PL, I see some of my NCOs as mentors and I'm sure a 2 star would still seek mentorship from higher. We can all learn something from each other. Learning is a never ending quest and everyone can bring something meaningful to the table.