Have you tried to call the airline directly and give your PNR # ?

Sometimes thrid parties maynot be able the assign seats, unless your flight is really full.

You can also tried a dummy booking on the airline's website on the specific flight you want to see if they have any assign seats open, or to see if it is saying to same thing like orbitz.

Also when you see 34 seats available, it only means they are willing to sell 34 seats, it maynot be the actual seats left, unless you can access airline's own reservation system or if you are a travel agent, you can't see the actual load is.