Traditionally published books:
Available in hard copy or eBook forms direct from the publisher, or from retailers like amazon.combarnesandnoble.comkobo.com and iBooks.
Independently published material:
Coloring books are available in paperback from retailers like amazon.com, barnesandnoble.com, and tower.com.
International booksellers that carry some or all titles:
Canada: amazon.ca
United Kingdom: amazon.co.uk
Australia: fishpond.com.au
New Zealand: fishpond.co.nz
Sweden: bokus.com
Prints and merchandise (not available...yet):
Art prints will be sold on society6.com in the future
Other merchandise will be sold via society6.com and zazzle.com
Handmade goods will be sold on etsy.com
Some items are carried in local retail stores. Check with your favorite gift shop, hobby shop, bookstore or other retailer to inquire about availability. 

Let me know if you want to carry my work in your store!