I think I killed all harpies including the queen when I come back in the area no more harpies spawn and I cannot complete the harpy traps quest ...

Inside the cave behind the doors at the bottom of the pit where you fight the queen no more harpies are spawning and I cannot complete the harpy traps quest

How about the place where there is a fairly downward-spiralling path (your medallion will respond to a few stones there) i.e. the Quarry. I remember a lot of harpies spawn there. You can trap those harpies too.

Btw the reason why there is no more harpy spawn at the area you mentioned is probably because you have completed the quest in that area.

Anyway I found a similar thread here:
http://www.gog.com/en/forum/the_witcher_2/harpy_contract_and_harpy_traps

Leave the area and come back later. The harpies do respawn.

If you meditate for 24 hours they will all be back!