A drum brake wheel will fit any fork. They can be pricey, so look for a used one.
A less expensive alternative is to use a side pull BMX brake on your fork. They look like
a brake on a 10 speed, but have enough clearance to work on a cruiser tire. You need only one hole in the crown of your fork to mount a BMX brake. Most cruiser forks already have that hole for mounting fenders.
I feel like the front brake is a necessity in case the coaster overheats, throttle sticks, of the clutch doesn't want to disengage as you approach a stop.

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"I don't believe in ghosts - but I'm afraid of them" - Mark Twain