"Recently I have tried approaching a few good developers through their blogs about various matters including advice on how to go about some projects I'm undertaking but I am surprised at the unfriendly responses I have received."

I have some experience in this, so let me try to explain a couple of things that I learned in the "school of hard knocks".

Once upon a time I was in a situation where I thought I could contribute to something one of the best programmers in the world was working on so I sent an email (I got the address from his webpage) and said something to the effect of " you say on this webpage you need this code and I could write it for you over the next few months because I am interested in what you are doing" and I got a 2 line reply which said (paraphrased) " A lot of people write to me saying they'll do this , but I've never seen any code yet so I am a little skeptical. Don't take it personally. Thanks. bye.".

So in the next email (sent a minute after I received his reply) I sent him a zipped file of code with an explanation that "this is what I've done so far which is about 70% of what you want" and he said "Whoa you are serious ...' and opened up completely, giving me a lot of useful feedback and very specific advice. I sent him a lot more code over the years. He is a (very valued) mentor to this day.

Another time, I was reading a paper from a (very famous) professor at Stanford, and I thought I could fill in some gaps in that paper so I wrote a "You know your paper could be expanded to give results X and Y. Do you think I should work on it?" email and I got a very dismissive one line email along he lines of " That is an old paper and incomplete in certain respects, Thanks".

So I sent along a detailed algorithm that expanded his idea, with a formal proof of correctness and a code implementation and he suddenly switched to a more expansive mode, sending friendly emails with long and detailed corrections and ideas for me to explore.

Now I am not in the league of the above two gentlemen, but perhaps because I work in AI and Robotics in India,which isn't too common, I receive frequent emails to the effect of "please mentor me", often from students. I receive too many of these emails to answer any in any detail, but if I ever get an email with "I am interested in AI/ Robotics. This is what I've done so far. Here is the code. I am stuck at point X. I tried A, B, C nothing worked. What you wrote at [url] suggests you may be the right person to ask. can you help?" I would pay much more attention than to a "please mentor me" email.

In other words, when you asks for a busy person's time for "mentorship" or "advice" or whatever, show (a) you are serious and have gone as far as you can by yourself (b) have taken concrete steps to address whatever your needs are and (optionally)(c) how helping you could benefit them.

Very good (and therefore famous) developers are very busy and have so much stuff happening in their lives and more work than they could ever hope to complete that they really don't have any time to answer vague emails from some one they've never heard of before.

As an (exaggerated) analogy, think of writing an email to a famous director or movie star or rock star, saying "I have these cool ideas about directing/acting/ music. Can you mentor me/give me advice?"

I am replacing the words "app" and "technical" in your sentence below with "film" and "film making".

"if I have an idea for a film that I want to develop, but my film making skills limit me, it would be nice to have people to bounce the idea off and have it implemented. "(so .. please mentor me/give me advice/make this film for me).

Do you think a top grade director (say Spielberg) would respond to this?

The fact that you at least got a 2 line response shows that the developers you wrote to are much nicer than you may think.

As someone else advised you, just roll up your sleeves and get to work. If your work is good enough, you'll get all the "mentoring" you'll need. "Mentoring" from the best people in your field is a very rare and precious resource and like anything else in life that is precious, should be earned.

My 2 cents. Fwiw. YMMV.