Where can I buy weaker gles?

I recently got my eye exam and a new pair of gles but I feel like if I wear the new gles, my nearsightedness will get worse. I still wear my old gles and I can still see fine and clear with them. I want to buy another pair of gles with my old prescription but I don't know anyplace. I tried asking my friend to send some to me from China but she said no....