I have several of the military whistles WWI to current. Got the MP bug a while back. I only know one person who has an eye as good as yours. Retired Navy Command Master Chief. Seems he can smell the neat old stuff.
He did share a yard sale trick with me. Always ask if they have anything military related. It has worked for me several times and I do not yard sale much (no self-control and very little room). Last instance I recall my question yielded a very nice haul of USAF insignia and patches. For some reason folks do not always put militaria out but are more than willing to part with it.