Hi - yes, yes and yes! My original HRT pill ran out after only 3 months on it - the second choice my doctor prescribed also unavailable, so I got to a third prescription which was available - this took several weeks to sort out as I kept thinking the stock would magically reappear, and it took time to get an updated prescription each time) - move on 6 months and now that is out of stock.
My pharmacist that I use is great and suggested to me a month before my pills run out to give him a call and he will check stock levels. I have done this only this weekend, and he called me back to say my brand of HRT pills is again out of stock (as are the other 2 previous choices) - but he had found another similar one available and has ordered that in and I just need to call my GP and check it is OK for me and get my prescription updated.
It is all a bit of a mad way of getting my HRT - but having gone without it for 6 weeks whilst trying to source appropriate pills 7 months ago I was suprised at how quickly my tiredness/ hot sweats & flushes reappeared.
My advice is call your pharmacist a month before you run out, find out what is available, then call your GP to update prescription (its the GP bit that takes the time as it may not be an appropriate HRT pill for you, then they try another and thats not available etc etc)