In case you are still looking then I have found some interesting links here:

http://rvdnieuwendijk.com/2012/05/29/powershell-function-to-get-disk-scsi-lun-number/%5B/url%5D

(See the comments too!!!)

https://social.technet.microsoft.com/forums/windowsserver/en-US/f9329531-6236-4c4e-9445-8cd7a165007b/getting-lun-for-a-cluster-disk-ressource-with-powershell

I hope that helps.