I wouldn't suggest cocaine since it isn't as safe and consistently formulated as a prescription med.
If Concerta availability is horrible and you haven't tried many of the other options that have generic versions, you might talk to your doctor about what options you have. I did not respond well to the newer, expensive ones but generic for Ritalin worked out well and that has some availability issues, but not as many as some of the others.
Adding to horrible availability, my friend also struggles with it and last time he talked about Livizux (LISDEXAMFETAMIN). Couldn't hurt to ask your doctor.