It completely depends on what companies you target, and the amount of "free samples" they have on offer, but for me, it's just been a luck game. For improved chances, make sure you don't just copy and paste the above letters, you need to make your letter as authentic as possible. If you fail to do that, then the company might not send you free samples for that sole reason, they'll know you copied it from somewhere.
While there are no guarantees whatsoever that this method of gaining free samples works, it has worked for me in the past, so I wish you all the best with your endeavours. If you've any other questions, feel free to ask! :)