@FlorinDinca Welcome to HP Community!
I understand that you would like to purchase the pen for the HP ENVY 360 15-dr1021nn.
1. HP Pen (Microsoft)
1MR94AA
SPS: 920241-001 (Dark Ash Silver) / 910942-001 (Natural Silver)
2. HP Tilt Pen (Microsoft)
2MY21AA
HP SPS: 929863-001 (Dark Ash Silver) / 929863-002 (Natural Silver)
Please refer to the following link supported pen for your product.
You could purchase the part from HP, use the HP Parts surfer to identify the part: http://partsurfer.hp.com/search.aspx
And order it via the HP Parts store: https://parts.hp.com/hpparts/CountryChoice.aspx?mscssid=&ccode=ZZ&lcode=ZZ
Or alternatively, Contact HP for setting up an order/service via phone support
Here is how you can get in touch with phone support.
1)Click on this link - www.hp.com/contacthp/
2)Select the product type.
3)Enter the serial number of your device or select let HP detect your product option.
4)Select the country from the drop-down.
5)You should see the HP phone support number or Chat option listed.
Keep us posted,
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Give us a virtual high-five by clicking the 'Thumbs Up' icon below, followed by clicking on the "Accept as solution" on this post,
Have a great day!