A PowerShell function to get the most recent used list. Note that this list isn't updated until you close the ISE.

Get-ISEMru.ps1

 Function Get-ISEMRU {

[cmdletbinding()]
Param()

<#
Path will be something like:
C:\Users\Jeff\AppData\Local\microsoft_corporation\powershell_ise.exe_StrongName_lw2v2vm3wmtzzpebq33gybmeoxukb04w
#>
$ISEPath = "$env:localappdata\microsoft_corporation\powershell_ise*\3.0.0.0"

Try {
    $folder = (Resolve-Path -Path $ISEPath -ErrorAction Stop).Path
}
Catch {
    Write-Warning "Failed to get ISE folder from $ISEPath"
    Write-Warning $_.exception.message
    #Bail out
    Return
}

If ($folder) {
    #construct the path to user.config
    $path = Join-Path -Path $folder -ChildPath "user.config"
    
    #verify the file exists just in case
    if (Test-Path -path $path) {
        #using -Raw sends everything at once as a huge string
        #and boosts performance a bit.
        [xml]$xml = Get-Content -Path $path -Raw

        #get the MRU setting as a string using an XPath filter
        $xml.SelectNodes('//setting[@name="MRU"]').Value.ArrayOfString.string
    }
    else {
        Write-Warning "Can't find $path"
    }
} #if $folder

} #end Get-ISEMRU