I'd second Phil's plug for the Software Testing Club website, and encourage you to seek out the mentoring group on there (although it does appear to be pretty quiet at the moment - perhaps it might be prodded back to life? I recommend it because that's how I ended up receiving some absolutely invaluable mentoring from Michael Bolton. (Who is, incidentally, an awesome mentor).
I would suggest it's worth considering what you want to know about mentoring. Mentoring relationships can be formal (arranged via a formal mentoring scheme, with training for mentors and mentees, a set timescale and goals for the relationship and formal support), or informal. They can be driven by the individual (I went looking for my own mentors), or be part of an organisation's training and development approach.
You might be looking for more information as a mentee - how do I find a mentor? How do I figure out if they're a good mentor? Should I be looking for someone with specific experience in my industry sector? How do I figure out what I want to learn from a mentor? Or you might be looking for more information on how to mentor someone - how do I find mentees? What sort of help and advice should I be offering a mentee? When does it cross the line into "doing their homework" for them? How can I get better at mentoring?
If you're looking at those sorts of general questions, then there's no need to stick strictly to testing websites for help - check out the Mentoring and Befriending Organisation. (Note: I'm not a member - which is free - but I participated in a mentoring scheme organised by a professional association which based their excellent training materials on resources provided by the Mentoring and Befriending Organisation.)
If you're looking more specifically for examples of mentoring in the software testing field, then I'd suggest checking out SummerQAmp - who are being supported with training materials by the Association for Software Testing. If that sounds interesting, check out Michael Larsen's blogpost asking for contributors.
Finally, I'll finish up by saying mentoring is NOT just training by another name. It's definitely not about providing someone with all the answers - or even with the questions. I like the definition the Mentoring and Befriending Organisation use on their website:
A voluntary, mutually beneficial and purposeful relationship in
which an individual gives time to support another to enable them to
make changes in their life
I'd definitely say that applies to the mentoring I've received through my career. (One mentor I only had one meeting with, but the question he asked me then led to me changing company about 6 months later.)