Not my find but i am sure some people would like to know. There is no video because i am not a view whore but it is very simple
1. Choose what paint you want, buy it.
2. Go to the metallic category but don't buy anything, now back out to the main selection menu
3. Change the color of your wheels or something but just exit the respray category
4. When you go back to Respray you should see pearlescent unlocked. I know it works for matte and metals, didn't test classics or chrome. Adding a few pics
classic black with lime green pearlescent