code:

clear
$model = 'MJ3T2LL/A'
$state = 'New Jersey'
$lastUpdatedTime = [string]::Empty
$storesJson = (invoke-webrequest 'https://reserve.cdn-apple.com/US/en_US/reserve/watch/stores.json').Content | ConvertFrom-Json

while ($true) {
    $availJson = ((invoke-webrequest 'https://reserve.cdn-apple.com/US/en_US/reserve/watch/availability.json').Content | ConvertFrom-Json)

    if ($lastUpdatedTime -eq $availJson.updated) {
        start-sleep -Seconds 10
        continue
    }
    $lastUpdatedTime = $availJson.updated

    $availability = $storesJson.stores | `
        where { $_.storeState -eq $state -and $_.storeEnabled -and $availJson.$($_.storeNumber).$model } | `
        select storeName, storeCity  
    
    if (!$availability) {
        write-output "$(get-date): Nothing available"
        start-sleep -Seconds 30
        continue
    }
    get-date
    $availability | % { "$($_.storeName), $($_.storeCity)" }

    start-sleep -Seconds 30
}