Haw Flakes are not made from the flowers of the hawthorn tree, but are made from the berries. The Hawthorn has berries called haw, and even the wrapper of the candy has a picture of a branch of the tree. The berries are mashed up, sugared, and then made into the little wafers. According to a few sources, the tree looks a lot like the holly tree, but the hawthorn tree only makes berries in the fall.
The three main brands that produce Haw Flakes are Bamboo Brand, Sunflower Brand, and Happiness Brand (which is made by Yantai Foodstuffs). According to this source: http://www.fda.gov/ora/oasis/12/ora_oasis_i_07.html, Haw Flakes have actually been banned by the FDA in Hong Kong.
You can buy Haw Flakes at most Asian supermarkets, or online at the following location: http://www.quickspice.com/cgi-bin/SoftCart.exe/scstore/snack-hawflake.shtml?E+scstore. They really are quite tasty and have a flavor similar to dried apple. Apparently there is such a thing as haw jelly, as well.
Sources:
http://asiagrocery.com/haw.html
http://www.etymonline.com/