My daughter just learned about Farkle and we were missing one die. She's used to playing with 6 dice and we only had 5. She asked if I could print one, and as any DIY father would say, "Absolutely!" Well the problem was that I couldn't find any normal size die on Thingiverse so I decided to quickly design what I consider to be a "standard" size die.
I measured an existing die using my calipers and it was about 16mmx16mmx16mm. Those are the dimensions I used to design in Rhino 3D. I'm still learning 3D design and Rhino, but I did print this design and it worked quite nicely.