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Where did you find Parallels? I've been looking for that for a while but haven't been able to find a version for Mavericks.
I already had Parallels 10 and simply upgraded to 11 which is the last version to run in Mavericks. However, there is a page to download old versions here: https://kb.parallels.com/5802 - v11 is there, but after you have downloaded it, you'd still need to persuade Parallels to sell you a licence for it (though you could try eBay and see if anyone is selling a copy?).
 
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