I have made a pair or two using grosgrain ribbon, and velcro. All I have done is cut the ribbon into flahes and added velcro the the back. I than use a strip of velcro (male and female sewn together so that it wraps around my calf and attaches) as the garter. Very easy to do and supplies can be found really cheap at any place that sells fabric (I got all this at Walmart for under $10 and have enough ribbon for a few more sets). This way you can also make numerous flashes in various colours or tartan and can just change them up with the same garters.

Here's some pics: