Those sounds are default because no skins pack is recent enough to include new planes. You will find the same problem exists for the 109G14 and the K-4, as it does for the P47N.
It's a very simple matter. Just copy the directory for the OLD spit9, rename it to spit16, copy it again, rename it to spit8.
Re-name 109g10 to 109k4. Then copy it, and rename that to 109g14.
Then copy P47D40 and rename it P47N.
There's probably a model I've overlooked, but those are the major ones.