Benzaldehyde is a know carcinogen, but then so are a lot of things we use
every day.  Bee-go must also be shipped as hazardous material.  Although I
have never specifically asked if the stuff was still legal, its use has been
advocated in meetings in front of the Maryland State Apiary Inspector and our
Extension Apiculturist.   Neither of them said the stuff was illegal.
 
Anyway, Benzaldehyde is available from Mann Lake (they have a website; search
on "Mann lake").   The catalog only lists gallons, but you can get quarts if
you call them.
 
W. G. Miller
Gaithersburg, MD