I'm clicking the links within <5 seconds of the ping, they're always gone!
Here's the trick I used.
Most of the stock alerts are for the same card - it seems they book some stock, it sells out, they book some more of the same stock later etc. So I added a card to my basket from a stock alert, it was out of stock by the time I got there, but next stock alert I just refreshed the basket to see if it was the card I had (it was) so just paid up.