you can get plates from Corning Costar. just fallow link http://www.corning.com/worldwide/en/products/life-sciences/products. You can buy both matrigel and plates from them. I did the assay with Breast cancer cells using 8 micron plate and it worked fine.
You can try this method: (for SCCi12 cells you can check literature how many cells to use)
Before the migration assay, I Serum starve cells for 1-4 hours. A volume of 150 μl (1 × 10^6 cells) from each sample was loaded onto the upper well. The medium (0.6 ml) was added to the lower well. The plates were incubated for 8 to 12 hours at 37°C in 5% CO2. After incubation, the porous inserts were removed, and the cells in the bottom chamber were stained ( (Hema kit, Fisher) and counted by using standard procedures.