Awhile back there were some posts and iddeals.com was mentioned. You can try it for free but it only lists flights out of AMS, you have to pay an annual fee to check other flights. It looks like it is under $20 USD per year.

I am not sure if anyone here is still signed up with them or not. Here is a post from last year
http://nonrev.net/general-discussion...lity-info.html

In that post this website is also mentioned (also with fee) ASU Travel - Interline discounts for over 40 years

Tony