If you are or can find a Klipsch Professional dealer, there are a few in-ceiling models with fire-rated back-cans. The speakers are nothing special; same as the contractor series, but the back can is nice and comes with a T-Bar bridge. If you can't find them, I have 4 SpeakerCraft backboxes that are set up for round speakers, but with minor modification (metal shears), will accept rectangular speakers as well. They are leftover from a job that ended up not needing them.
Note that if you are installing in a garage ceiling, you MUST use a two hour minimum back can such as those mentioned above. The Klipsch cans will retrofit, but are very deep, the SpeakerCraft backboxes are larger and need to install prior to sheetrock.