Why do we only find fossils?

I think you'll have to modify the "never".I have held in my hand a tyrannosaur fang that the researcher in the preparation lab said was the original (or mostly) tooth not mineralized replacement.I think that for things as recent as under 100 Myr ago there may be some bone that is not replaced but I don't know for sure.I think you are right about the trilobites etc. I'd suggest finding a reference talking about shell material from the time of Egypts height.

Note, Yaro, what RM says: The thing to note is that the example he is refering to is not blood.

You might point out that this is wrong if RM is refering to the Coelocanth; the current one is not the same species as the extinct ones; it is not the same genus either. I think it is the same family.

What seems to me to be missing in the discussion to-date is the state of bones found from the last few 1,000 years. These are what, in the YEC view, I would think all bones are supposed to be like.I've found some bones on the surface (deer, cattle, rodents, cat) that were almost certainly less the a decade old. They are the original bone (to my eye) but significantly weathered in many cases.Obviously these aren't really good comparison since I only found them because there were on the surface. I'm interested in bones, shells etc found in middens, tombs and the like.

It's a start but no real detail on the nature of the fossils. Mammuthus' reference is on the right track.It appears that for most cases the permineralization is rather slow or doesn't happen. There are special cases where it is quick.What we seem to have is this:
1) There are many bones of various sorts that are less than a few 1,000 years old and are NOT mineralized at all.
2) There are many bones of many different animals (dinos etc.) and ALL of them are mostly or completely mineralized.YEC'ers have not supplied an explanation for this that I am aware of.

I don't think that is the point of this thread.What is the point is that for a large variety of animals, all over the world we only find them as fossils, heavily permineralized (and therefore on your borderline between fossil and not) or preserved under very special circumstances (in amber for example). We find none of them as simply "old" bones.