I have moved your post from the original topic you replied to as it had no relation to that post.
As the manufacturer of these handset's I can only provide you with the part number as follows:
Replacement Handset and Cord for CX500/600 IP Phone, 5-Pack.
These come in packs of 5 and you would need to find a reseller to sell you an individual unit.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services
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