Unfortunately, we don't currently have a way for you to sort the projects list by last name, but we'll add it to our backlog - it would clearly be very helpful, along with search by project author, for your case.
As a workaround, given the current state of things in Cloud - would it be easier to work your way sequentially through the list of projects in Cloud's order? I'm guessing looking up the corresponding student in your alphabetically ordered grading list would be quicker than searching by "eye" through Cloud's project list.
A question for you - would a view along these lines be helpful?

Thanks,
Robby