Where to buy:
You can buy the Trimorphs at Amazon.com ...
Kindle version: here
Print version: here
It is also up on all the other Amazon stores, but I can't include all the links here. A search for trimorphs will find it, I hope.
If you need an epub version you can get one from Kobo here
or, if you prefer, from the Nook here
The audiobook version is up at Podiobooks here
You can also buy the print version from the Bookpatch here