Looking through a few Japanese-English dictionaries, the letter "P" section is full of mainly 外来語. I didn't find this pattern with any of the other 25 letters of the Latin alphabet. I've read that the Japanese have an aversion to names with certain sounds or syllables in them, is this a similar case with the "P" sound?

I haven't studied much on historical pronunciation/phonetics, but likely the p* sound never existed independently in Japanese until relatively recently, except when caused by rendaku (voicing of a h* in compounds).