I just checked with Challenger, here is their reply:
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Thank you for reaching out to us.
We are pleased to share with you that the Apple Watch Series 3 will be available with us and at the following outlets on Friday, 22nd September 2017 onwards. It is with regret to inform you that there will be no reservations allowed and it will be a first come first served basis.
Challenger Ang Mo Kio Hub
Challenger Bugis Junction (Flagship Store)
Challenger Bugis Junction (Level 3)
Challenger Clementi Mall
Challenger Changi City Point
Challenger Causeway Point
Challenger Great World City
Challenger IMM
Challenger JEM
Challenger Jurong Point
Challenger Lot One
Challenger NEX
Challenger Parkway Parade
Challenger Tampines One
Challenger VivoCity
Should you require any information or assistance, please do not hesitate to contact us.
Thanks & regards,
Leon
Customer Care Support