Write it yourself? Seriously, there's nothing preventing you from putting a module up on CPAN that does what you're talking about. Personally, this sounds very much like what the various XML-RPC modules (Frontier, RPC::XML, etc) do.

As for syntax, you'd have to use $order->item and $order->ALL->price or something like that to make is legal Perl. Or, you could do what stvn has been doing in his P6 Object Metamodels, which would translate into E4X for Perl like:

my $e4x_parser = E4X->new( ... );
my @items = $e4x->get( 'order.item' );
my @prices = $e4x->get( 'order..price'; );
[download]

You get the idea.