To get a list of all available font families on your system, you can load the .NET drawing library and then ask the InstalledFontCollection for all font families:
[System.Reflection.Assembly]::LoadWithPartialName("System.Drawing") | Out-Null
(New-Object System.Drawing.Text.InstalledFontCollection).Families
(New-Object System.Drawing.Text.InstalledFontCollection).Families
You can easily use this to check whether a specific font family is available, too:
[System.Reflection.Assembly]::LoadWithPartialName("System.Drawing") | Out-Null
$families = (New-Object System.Drawing.Text.InstalledFontCollection).Families
$families -contains "Wingdings"
$families = (New-Object System.Drawing.Text.InstalledFontCollection).Families
$families -contains "Wingdings"