Use a Mistral with accents that match the components, and make the barrel closed end.
You will struggle to find a kit pen that tapers the cap to the same extent as the commercial pen in your photo Steve, because the constraint is always going to be the requirement for a tube inside it. I've tried to create a slender pen with a taper in the cap, which I have done in the form of the Leveche, but without making the centreband oversize, and therefore loads of meat at one end, tapering to next to nothing at the other, (and therefore a heavy cap), as I say, the tube inside is the limiting factor.
If you want that kind of taper you are talking either kitless, or on a kit forget the cap finial, shorten the kit tube inside and make the cap closed end too. (which means you won't have a clip either)