Found the design and modified it for my use. I added a small socket to print it upright. With my parameters, the dartcup fits immediately i a 10mm aluminium tube. All you need is a steel needle. Got mine from ASMC, but they don't have them anymore.

Found the needles again: Search for “Fox Outdoor Nadelpfeile” on Google or on Amazon : https://www.amazon.de/Fox-Outdoor-Nadelpfeile-Blasrohr-Display/dp/B06X9RMCW4