I am an avid stamp collector. So Many different collections to choose from. 
It has been a popular hobby as long as stamps have existed.  I've been collecting since I was 6.
Have you ever tried to sell any for profit?!
Unfortunately all the stamps I have are used so not very valuable past the proof of paymeny cost. 
Are there in hard to find ones that you are still looking for to complete a collection?
I really want the Washington-Franklin issues since it was a huge change by having two silhouettes instead of the traditional singular.
How do you go about finding it? 
If I couldn't find it online I'd probably contact a university philatelist to see if they had any leads on where to find them.