Per PCI mandate, VeriFone cannot manufacture overlays for the Vx520 or any PCI 2 or PCI 3 equipment. Some processors have chosen to make their own so you can check with your processor or your processor can provide you with a QRG (Quick Reference Guide) that will show how to use the terminal.
Here is a note from VeriFone about why they cannot make overlays for Vx520 devices.
When all is said and done, we as a manufacturer cannot provide or apply overlays for any of our PCI 2.0 and 3.0 devices that have PIN Entry capability as it is in violation of the new requirements. The highlighted PCI Security Standards link will take you to a Q/A page related to PCI 2.0. Page 4, Question 10 speaks to the use of Overlays that cover the pin entry area on Pin Entry Devices (PED). The QRG’s (Quick Reference Guide) provided by processors are excellent reference materials in the absence of an Overlay.
Q 10 Does the use of protective keypad overlays impact the approval status of a PED?
In general, overlays are not supported by the PED approval program due to the potential for keypad tapping. Overlays may be used where they do not cover any portion of the PIN entry area. For example, in a touchscreen device whereby the touchscreen is used for both signature capture and PIN entry, an overlay may be used to protect the signature area from excessive wear. In this example, only the area used for signature capture may be protected. The material used must be transparent, and not merely translucent, so as not to obstruct the key entry area when viewed from any angle.
Click here for PCI PED Technical FAQS.