How annoying! This really does reflect the deficiencies of the tools available. Sadly, I do not know of a currently functioning tool which searches Avios partner availability directly. This is a problem we share because I also want to book JAL F rewards over long periods and this is a constant battle with broken systems!

I called YouFirst who confirmed that there is no JAL availability tomorrow from London on Avios, as BA.com also says. I then checked via the AA website which suggested it was totally bookable. I just called AA and the agent checked if she could secure the space, and was able to. Pity about Avios in this case. BA and Alaskan can't see the availability, so it's not just BA.

My personal guess from the past, having observed this before, is that this is American Airlines's booking tool mucking up so badly that it makes JAL F bookable for points. Either that or AA and JAL have an agreement, although that seems far-fetched. This could be JAL/AA JV related but who knows!

Bear in mind, I had to ask the AA phone agent to check LHR-HND directly, as it did not come up under LHR-TYO, but LHR-HND worked! Therefore, it is probably just AA's computers melting - nevertheless an F seat bookable with AAdvantage.

By the way, Alaskan's flexible dates/award calendar view is useful because the availability is exactly the same as BA and one can see month-by-month, however that tool often just refuses to work!

On the plus side, it seems JAL are back to no longer restricting redemptions a few days away to 1 seat, which is great. CDG-TYO on the 12th of July is in fact for 2 F seats.

Given the parameters you describe about the 29th of March, I'd suggest just setting up some seats.aero alerts, perhaps via another search tool as well, and hoping F gets released within 14 days. Also set up some alerts for business class direct from European points. There's really no alternative apart from hoping seats come through or paying for an upgrade. However, the seats are fairly likely to release, so good luck!

The main lesson is that one has to meticulously check availability and then pounce on it. Hopefully the mileage broking situation should abate by next year, as demand from people who have been unable to return to China to see family calms down, and JAL and others add anti-scraping plugins to their websites.