Pen for Cintiq 13HD DTK-1300

Hello, I have recently lost my pen for the Cintiq 13HD. It is a great product that got handed down to me from my dad, as he bought it in 2013. It still works perfectly fine till this day and I have no issues with it. Unfortunately, I have lost the pen and have searched all over the internet for a replacement, with no success.

It does not feel right to me to buy a completely new tablet and pen, simply because a perfectly working old one.
What would you recommend? Are there any pens still available/in stock that are compatible with the Cintiq 13HD?

Thank you for reading my message. I hope to hear from you soon.