There isn't any way to get Kindle files at no cost to you, if you are exclusive to Amazon. You can buy them and 'gift' them to reviewers (recouping 70%~ish of your expense in two months), you could send them as an attachment, using the file you uploaded. Or, if you aren't exclusive and are using Smashwords, you can create a coupon code to share with your reviewers, who can then download it from Smashwords.
Of course you can get your kindle file for free.
Log in to your Bookshelf.
Mark the checkbox of the book you want to download.
From the Actions pulldown menu, select edit book details.
Scroll down to item 6(Preview your book).
Select Download book preview file.
Now you have your book, and you can give it to whomever you wish.
You should be doing this for every book you upload prior to publishing it. You need to open the book in the dowload loadable Kindle Previewer, and verify that your formatting is correct in all the device emulations prior to hitting the 'publish' button.
Please clarify that very last stage! I'm very familiar with the previewing process during upload. But tell me this. Once I've got the book open in the previewer, how do I then "give" it to someone else? Please describe that bit precisely.
Follow huemann's advice, including the key step of downloading the file for previewing (not just previewing it at the Kindle site). Now you have a copy of the Kindle-formatted book on your own computer. You can email it to anyone who has a Kindle (or a Kindle reading app on their computer).
The bookfile is in your computer files. (if you use Windows, it's My Files/My Kindle Content/then search by date you downloaded, as it has a numeric name, not the book title). That's the file you'll either convert with Calibre to other filetype, depending on what the reviewer reads on, or what you'll attach directly to send to the reviewer. I hope that helps answer your question.
What you need to do then is personalize the copy you send to people.
It's easiest to do this with html or e-pubs directly in their respective editors, but you can take your mobi and unpack it too. On your Title Page, under your book's title, put in brackets "john doe's review copy," Repack your mobi, and send to john doe. If he illegally distributes it, it'll be real obvious. That's manual DRM.
This is one of the reasons why I create e-pubs using Sigil freeware. You can drag-and-drop the e-pub directly into the downloadable Kindle previewer, and it gives you your mobi right there on your computer.
The truth is, is that you will need to download a PROOF COPY of your book. Usually it seems as though this access is done right before publishing your material on create space and Kindle I think too. The process in downloaded this PROOF COPY of your book should send the file directly to MS Office on your computer if you have it. It won't be a hard copy you'll have to send them but, it will be the complete revised version of your book which will be something for reviewers to be able to at least look at, and the PROOF COPY is free!
How can I unpack my mobi file? I downloaded it as per your instructions and downloaded Sigil as well as the Kindle previewer. I opened my mobi file with Sigil and it just showed the title with underscores between the words. Is this the page where I define it as a "Review Copy for John Doe"? What am I missing here? Thanks so much for your help. I searched a long time before finding your advice which was exactly what I needed.
The best way is to by pass freebies through Amazon all together. GoodReads is the answer. Amazon bought GoodReads for a reason... It has very dedicated readers. Far more than Amazon. People are more apt to review your book on GoodReads than they are on Amazon. If you do a google check of your book, GoodReads usually beats out amazon for the review.
Become a GoodReads author and you can give away your book to people who request it. You can give away 1 or 100 and you choose who receives them. You can choose them randomly, or, (the better idea), select those who have the biggest following with the most creative reviews. Let them market your book for you!