It's doubtful that you will find anyone who gives away free reseller accounts, as what would be in it for the provider?
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Perhaps you can find limited free trials and other promotions that would give free reseller account for a number of days/months, but you cannot expect to receive a free reseller account from anyone and think that it will be at all reliable.
Well, in the cPanel reseller account sense, I doubt there are many who offer it for free, and if they do, it's likely a very small account that isn't a real platform for reselling, just an account to know what is in store and learn the ropes.
However, in the start-selling-hosting-with-zero-dollars upfront costs, resellerspanel.com offers such a possibility.