BertieBadger

Not 100% sure on the ExpertFlyer issue sorry, I thought the free version was seat info only but rapidex suggests otherwise. Maybe some confusion between the free seat alerts version and the free trial of one of the Pro options?

For occasional queries, there is a dedicated thread to that where someone with a Pro sub can look it up for you. Find it here: Help to check BA seat availability and BA flight loads

That tends to be more used by people flying in the immediate future and trying to read the runes regarding their free upgrade chances, but the info is the same. At the wiki at the top of the thread you'll also find links to other tools that can glean this info.

One further free method (not listed) which doesn't give you direct availability info but which you can use to infer it is ITA Matrix, which lets you restrict your searches to certain booking classes, but that's obviously a pretty slow method - e.g. you would need to look for 1 passenger restricted to A class, then 2 passengers and so on depending on what info you were trying to clean. But as a stereotypical Scotsman when I have some flexibility in my travel dates, I do find that useful as I restrict the searches to find fares in the lowest buckets (T,I,A)