I hope this won't derail the thread...
I have started to just sand the taper onto parallel graphites. I have a belt sander, which makes it super easy. I'm not sure how easy it would be otherwise. Maybe the low cost way would be to chuck a sanding disk into a drill, clamp the drill in a vice, and turn the tapers on the spinning disk. I would advise a medium grit, like 100 or a bit finer.
How much to taper? Easy, just keep test fitting until they go to the bottom. If you press & turn while test fitting, the high spot will acquire a sheen. That tells you where to taper some more. With Pings for example, all of the taper is in about the bottom 3/8".
There just aren't that many taper options in graphite. And most of them start out as parallel and the manufacturer sands the taper onto them. I hope you find some, but if not, think about the DIY route.