Booking tool?
 

I'm trying to build a multi-city itinerary on Croatian Airlines (and possibly LH). The itinerary will be BRU-ZAG, DBV-FRA. I can find the fares that I'm okay with on ITA, but I can't book the fares anywhere. Croatian Airlines website apparently does not offer the option for multi-city bookings and when I price the flights as one-way the fare is nearly double.

I can't get the same fare on Expedia.com or Travelocity.com. Does anyone have a suggestion?

I'm totally new to *A airlines.

Thank you.

How about a brick-and-mortar travel agent?

You could also try orbitz.com they are usually quite useful in reproducing fares found on ITA.

Hope this is not too late, and helps, cheers,
G

Some times you just have to talk to a human. Websites are pretty basic in their abilities to book flights.
As mentioned talk to a travel agent in a local shop OR call the airlines reservation #. If you get someone that knows what they are doing all you do is read them ITA #s and routes and they can pretty much book your trip as requested.