The BA97 Calendar should work for you.
https://ba97.com/calendar.asp

I helped create it with the guy "BA97" himself almost 15yrs ago. You can add your FF membership status levels to you profile (plus Priority Pass, Amex Platinum etc.) and when you put in the origin, destination, airline and class of travel for your flight it shows you the lounges you can access. Admittedly I haven't assisted with it much since it first rolled out but it's a clever interface.