Where to get keys made
You can go to an auto locksmith
Ace hardware also may cut car keys, if you have one near you..
Unfortunately with gen 1, 2, and 3 mini coopers are all computer chip keys, and while all are laser cut keys, because of the chip, I've never seen a hardware store that can program your car to recognize the new key. you would be able to unlock the car but not start the engine because of anti theft feature. So you really are left with Locksmith or Dealer and both will charge 200-300 usd for the new key and programming. Although i have heard of ePay sellers who can hack keys... never felt comfortable trying that route though.
Typically you need two working keys to program another one. With one or none you will need a Mini dealer.
Looking for a Used Cooper in your area?
CarGurus has 602 nationwide Cooper listings starting at $1,300.
Search MINI Cooper Questions
MINI Cooper Experts