I use tapered end mills for the finishing pass and path engraving pass on my terrain relief model carvings. They get me the detail of a very small ball-nose end mill but with much longer reach, allowing me to make deeper carves without crashing the collett into the walls.
I use PixelCNC to create the toolpaths, and then I run the G-code using Carbide Motion.
As for procuring tapered mills, I use basically the same ones as Stuart gets on eBay, but I get mine at Amazon in various sizes. (They’re probably from the same source in China, so it’s just whatever source is convenient, really.) Basic two-flute 1/4" shank, 31.75mm flute length, with whatever taper angle geometry requires for a given tip radius.