Availability usually good. Key thing on BA is to use the Search and Book section rather than Reward Finder (or whatever it is labelled) - otherwise partner airlines (i.e. JAL, CX etc) won't show. I've had several JAL or JTA domestics using avios and regional flights (e.g. HND/NRT - HKG) are also good value (especially in J). Availability tends to come and go a bit so keep checking.
Regards
PR