This guy implemented HashMap among other things.  Looks like you just have to cut and paste the listings to get it.
http://www.ericfeminella.com/blog/actionscript-3-apis/

The real problem is, you should be able to iterate over an associative array and get it’s values using array syntax.  I don’t want to call HashMap.put(key, object) and HashMap.get(key) every time.  I want to create an object declaratively like

var foo:Object = {myKey:myObject, anotherkey:anotherObject};

I then want to pass the keys to a dataProvider with foo.getKeys() or retrieve data with foo[‘mykey’].

I tried creating tacking a function onto the prototype

Object.prototype.getKeys = function(){
  var keys:ArrayCollection = new ArrayCollection();
  for each (key in this)
  {
    keys.addItem(key);
  }
  return keys;
}

But that didn’t seem to work.  (obviously we don’t want to add getKeys() to Object, so I’d create a class that extends Object, only I can’t find out an easy way to pass the literal instantiation

{myKey:myObject, anotherkey:anotherObject};

to the base Object.

Here’s another rant about actionscript and collections:

http://blog.iconara.net/2007/11/25/architectural-atrocities-part-8-is-there-no-equality/