Not everything has been mapped yet, so you either have to wait until someone does, or figure out and submit it yourself to MCPBot (or something like that, I haven't really done any messing with that stuff yet, I just use what they gimme )
http://export.mcpbot.bspk.rs/ has the latest/stable mappings. I just use the (close to) latest one, has more stuff mapped, and someone said somewhere that the snapshot ones don't get broken very often so it's relatively safe to do.
If you're not using 1.15.2, I'm not sure if using the 1.15.1 mappings is bad or not for 1.14.x (or if it even works). I just do everything in the latest version myself.