We just took this trip aiming for Oneworld J for an identical cruise. Flew on AA award over MCO-MIA-LHR-BCN (last leg on BA). Like pulling teeth to get J award space though. F was easier (got 4), then as it got closer Y opened up. I only ever got 2 J ~ 250 days out.
On the way back we flew AB VCE-TXL (stayed overnight) - ORD-MCO. All in J. AB only ever released 2 J to AA (there were 4 empty seats when we boarded), but it was a J/F flight and it was their new J so it easily rivaled AA F.
You really need to keep your city pair options open. At 330 I started checking every route through MIA, JFK, ORD, etc... MIA-BCN did open at one point as well. Don't expect availability at 330 though. Flying in Oct may give you an edge at least. We flew peak June/July.
Availability on AA (and partners) can be had, but I bit the bullet and also subcribed to KVS which I checked every single day. I hate the lack of a notification feature like EF, but liked their access to AB unlike EF.