Actually, these you can't. I searched all over ebay - there are lots of replacement feet, but none this size. These feet are glued on, but because this laptop runs so hot, the heat loosens the glue, and then the feet can just slide off. With the original back cover, One went missing, and the second had slid about 1cm to the side. It doesn't matter how careful or careless you are sliding it into your work bag, they will come off.
I bought a Dell Inspiron 7359 about 6 years ago. These had the exact same tiny rubber feet on them, I could not ever find a replacement. With that unit, 2 of the 4 feet were falling off and I'd have to stick them back on again. It was very frustrating. The only option was to replace the entire back cover, and then use those as replacements. I think I used superglue to re-glue them back on, and I never had a problem again. Dell wanted $99 for the replacement feet.
In this case, it was covered under warranty, and Dell replaced the entire back cover with a new one.
You can always purchase replacement bottom covers... technically shouldn't be covered under warranty unless it was a defect. Being rough and careless with your laptop, the rubbers will fall off due to wear and tear.
Yes, they are sending a technician to replace the back cover of the laptop. That's cool and all, thanks, but what happens after my warranty runs out and the next set of rubber feet fall off? Wishing there was an easy replacement that didn't involve Dell Technical support.