James,
 
You have discovered one of the neat things about fossils.  The
difficulty of getting a really good, clean specimen makes it all the
more valuable (not monetarily but to the intrepid collector).  If you
decide to mess with them I recommend getting a book on cleaning them
first.  A Dremel tool and patience are the best tools.  Using acid will
certainly work on limestone but it is VERY HAZARDOUS and you had really
best get some experienced adult help.  Just handling the stuff is
dangerous, breathing the fumes is deadly, getting any on you will
quickly burn (that bubbling will be your skin going away), and then you
have to figure out what to do with the stuff when you are done.
Sometimes it is really better to leave the fossil in the matrix.  I have
a lot that way and they look great.  I also like them free and cleaned
but it is just not always possible.  So go slow with this, okay?
 
Tom Eichhorst in New mexico, USA
 
P.S.  I got a few together for you and will mail them tomorrow.  Nothing
spectacular but brachiopods have always been a favorite of mine and I
think you'll like them also.