$webapplication =  Get-SPWebApplication  “url of your site collection

foreach($site in $webapplication.Sites)
{
foreach($subWeb in $site.AllWebs)
{
if( $subWeb.AllProperties[“WebTemplate”] -eq “WebTemplate Name“)
{
Write-Host “Site url :” + $subWeb.url
}
$subweb.Dispose()
}
$site.Dispose()
}