If you have an android phone you can use google play store to download it and then move the apk file from your phone to your Fire using BOX or other cloud program
You can directly go to the Google play store using your Fire as Amazon has forbid you do to that directly (direct competition to their store).
I use Go Launcher EX just fine on my Kindle Fire (1st Gen)
Im not sure if the new HD is different and has been changed to not allow this
Its great and I can still switch back and for back to the Kindle Launcher/desktop to allow me to access my Amazon apps, movies, books, and music, which you WILL want to be able to do.
Try asking on the Go Launcher thread here for more help