Like most people ive spent hours searching through every harp i own trying to figure out what key a given song is in. One of my favorite songs "one way street" by Aerosmith took me for ever to find the key, as I couldn't even find it on the internet. so after waisting money on 3 or 4 new keys i found out what the issue was:

Check those bent notes!

I couldn't find the key because 90% of the notes in the song start at a half bend, now maybe this is commen sense to some of you but it was a huge break through for me.
I've posted my tab for the song on this site (good luck trying to read it tho, i did my best to legably tab those half bends)

I feel your pain!!

I tabbed "Sometimes I Think About" on this site. Listen to the way it's sung (You Tube link in the tab). That was hard as heck to figure out.