SAN-NRT has 2J for JL on 5/24...

NRT-HKG has 3J for CX on 5/26...

HKG-DPS has 2Y for CX on 5/27...

(or you could wait until 5/28 if you simply MUST have J for a 4 hour flight for a KA flight then.)
(You really need to be doing a segment by segment search on BA, the CX flight HKG-DPS isn't timed great for a lot of USA connections so you might miss it doing a USA Gateway-DPS search. Also, CX availability has dried up a lot now that everyone is buying cheap US miles to fly it, and there aren't 744s with 9F cabins flying to the USA any more.

Your best bet if you are feeling "lucky" is to wait until a week or less before your travel dates, historically, F and C partner awards will be opened up by CX close-in if the cabin is unsold. You may want to invest in Expertflyer.

)
Um, so do Thai (TG) and Singapore Airlines (SQ). TG avail to DPS from BKK is pretty good, so is SQ availability. SQ uses regional equipment for a lot of Asia that is available on redemption: it won't be visible on the UA site, but it's there i
f you search using the ANA tool. Their SIN-DPS service is all on regional planes (4x daily), so available as part of a UA redemption (but UA horribly penalizes you for flying partners with really huge mileage burn

).
PS: OP can
transfer Chase to SQ and use SQ Krisflyer to fly to or from DPS... potentially in SQ Suites class or SQ F on the longhaul segments.
PPS: OP, you do realize that there will be a cash outlay for the infant-in-arms, right? Often it's 10% of
the cash fare. Be sure you are careful about that, I've seen nightmare stories on problems with lap children tickets as part of UA awards being screwed up in the UA forum on FlyerTalk...
PPPS: Personally, having your US miles turn into AA miles and giving you a balance of over 500,000 miles to work with doesn't sound so terrible, given your requirements (multiple seats, infant in arms). Might help if you did OW one way and *A the other, with BA for positioning. Since US doesn't do one-ways...

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