I'm a member of the International Perfume Bottle Association - have a look at their website and consider joining.
Passion for Perfume is an American site that lists perfume bottles for sale. Janice is the moderator and sends an email every couple of months when new things have been added to the site. It's always worth a look.
Periwinkle Antiques in Western Victoria always has a selection of interesting perfume bottles and compacts for sale.
Grace is an expert on perfume bottles and has an identification and appraisal service which I have used myself for one of my more unusual finds. Check out her site.
Mike from Sydney, Australia is researching some of the early powder and cosmetic manufacturers and has a fantastic blog with some great stories and images of early powder boxes, compacts and the characters involved in these old companies.
Kigu compacts have many examples of their great compacts on line so you can work out the name of your example and get an idea of when they were made. The history of the company is also very interesting.
This is the site for British Compact Collectors Association. It's a good site with lots of information.
To learn a little more about Lydia Pinkham read her page on Wikipedia