Hi Eduardo,
Your best bet for sourcing books over the internet is:
www.abebooks.com which links an enormous amount of new and secondhand book sellers.
I've used abebooks a huge amount as I have lived in Arctic Norway and am now in Chile, so I have to use the internet to pick up nearly all my books.
I have never had any problems with an abebooks listed seller and I must have purchased over 20 or 30 books using it.
In terms of uniform related books and so on, I'd still recommend the Osprey volumes. Terry Treadwell doesn't have a fantastic reputation so I'd be suspicious of any works by him.
In terms of a general work on the airwar you can't go past Alan Clark's "Aces High" which is a good overview, tons of pics and the very nice (although sometimes erroneous) paintings of Michael Turner. Just make sure you pick up the 1999 reprint.
Good luck with the book hunting and welcome to the 'drome!
Junior.