Paddington tickets

Hello, my wife and are visiting London in September for the first time in two months and were really excited to see Paddington, just to see it was completely sold out two months in advance! I was surprised to see that when there are available tickets both before and after. I was wondering if there were any other sites (I looked at today tix and London Theater Tickets) which I should use to look for tickets or if I’m just out of luck. Thank you all!