Does anyone know where I can buy copies of Enid Blyton's "The Famous
Five" or the Secret Seven set a books?

Hi! Thanks for the question.

You could buy "The Famous Five Series" from the following sites. The
Dooyoo page also has price comparison before you could buy. The prices
are all in British currency. The books are from Amazon UK while the
audio book versions are being sold by WH Smith.

Dooyoo: Price Comparisons
http://www.kelkoo.co.uk/b2b/shopbot/search.jsp?from=shopbot&partner=dooyoo&catPath=uk%2Fbooks&catId=5101&title=Famous%20Five%20books&author=Enid%20Blyton&isbn=&maxprice=&x=14&y=9

You can also find other Famous Five products in the next website:

The Famous Five
http://www27.brinkster.com/fiveonawebsite/intrestinginfo.htm 

The Secret Seven series meanwhile can also be obtained from the Amazon
UK site.

Amazon UK
http://www.amazon.co.uk/exec/obidos/ASIN/0340569808/topbooks0b/202-6312511-4160637

You could also buy it second hand from Badger Books

Enid Blyton books for sale
http://www.janetnic.freeserve.co.uk/blyton.html

Search terms used:   
"Enid Blyton" "Secret Seven" "The Famous Five" 
  
I hope these links would help you in your research. Before rating this
answer, please ask for a clarification if you have a question or if 
you would need further information. 
  
Thanks for visiting us.  
  
Regards,  
Easterangel-ga  
Google Answers Researcher

Hi,

Here are some used books search sites - Bibliofind is a good place for
comparison shopping:

<http://www.abebooks.com> 
<http://www.tomfolio.com> 
<http://tinyurl.com/20q4> Children's category at Tom for browsing.
<http://www.bookfinder.com> Searches several sites but often doesn't
show all results.
<http://used.addall.com/> Also searches several sites but often
doesn't show all results.
<http://www.zshops.com> 
<http://www.bibliophile.net>
<http://www.bookavenue.com>

hummer