The only place I can think of where you can obtain that information is the Multiple Listing Service. For that, you need to be a member, but you could ask an agent to obtain the information for you. I cannot think of any reason why an agent would not be willing to give you that information, so just ask one.
There really is not a concrete value in knowing the asking prices. There are different strategies in developing an asking price, plus a lot of properties start out over-priced to begin with. Comparing properly priced houses to over-priced houses, then lumping them together in some sort of analysis would skew your figures.
I can see how you could intend to use such knowledge for the purposes of negotiation, but with an informed listing agent, it should be a fairly ineffective strategy.
For example, recently I saw a web site where the agent was hawking his ability as a listing agent. He said the average home in his area sold for 93% of asking price, but his average listing sold for 97% of asking price. The implication was that he got more money for his sellers.
The truth is probably just that he priced his homes correctly to begin with.