They're available in most drug stores in the foot aisle. If you don't see one, ask the pharmacist. Basically,it's just a regular cushioned heel lift with a 'doughnut'hole in the middle of it. So even if they don't have them, you could do it yourself by cutting a hole in a regular cushioned lift.You may have to wear a lift in the other shoe for the time being to balance things out(so as not to cause any imbalance issues).
For me the pain as well as the lifts were gone in about a week. You should also do exercises to strengthen your shins which are frequently weak in runners as compared to the calf muscles.