I bought mine from Bike Tyre City (The Bike Doctor). They're not cheap, considering what they are, at $80 but I think it's worth it for peace of mind.
Another option is the Xeno disc brake lock with cable. The lock is alarmed with a 110dB that is ear splitting & definitely grabs the attention of anyone around. Steve does sell those.
Now to be found "working" at Ace Scooters (sales, accessories, coffee maker, dish washer, gopher and general stirrer).
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