I can recommend De Atramentis Document (permanent) ink cartridges for use in Kaweco Sport pens.
I use them in a Classic Sport and the combination is very good for drawing.
No problems if they aren't used for ages either. If you are not worried about the ink being waterproof then both Kaweco's own inks and Diamine's are very good.
It may be my imagination, but the Diamine's seem to flow a bit better.