Swizzy has released a great tool for unlocking the Parental Lock on your 3DS/3DS XL, heres the details:
****************
* Requirements *
****************
- Microsoft .net framework 2.0 or later
- a Nintendo 3DS
********************
* What does it do? *
********************
- It'll generate the master key for you to unlock your parental locked Nintendo 3DS
********************
* How do i use it? *
********************
1. Forget your pin for the parental controls of your Nintendo 3DS after you've locked it
2. go to System Settings (you may have to launch it in 2D mode)
3. Go to Parental Controls
4. Click on Forgot Pin
5. Click on I Forgot
6. Write "Enquiry Number" into the "Servicecode" box and click OK (NOTE: Make sure the date set in the tool matches the date on the 3DS!)
7. Click on GetCode this will generate your key
8. Press OK on your 3DS and type in the number then press OK again
9. Do whatever it is you needed to do once you had unlocked your 3DS
***********
* Credits *
***********
- Thanks neimod for uploading the original source code: https://github.com/3dshax/ctr/tree/master/parentool