"Lung Plush from I Love Guts: I Lung You!" are available from Amazon.com Toys & Games. These toys look cute and are generally found to be interesting by the pediatric patients.
More info here: Lungs Plush Toy from "I Heart Guts, Love Your Insides":
This adorable, super-soft, 9" x 9" lung is perfect for cuddlin', and makes a great gift for anyone who needs some extra breathing power. Comes with a handy tag telling you all about your lungs. Safe for all ages. Designed in California, made in China.
I already have the dust mites by GIANTmicrobes from Amazon.
Educational Toys for Allergy Clinics