I think you're on dicey ground in general getting teachers to recommend you in a professional context (a recommendation to another school is different).
A teacher has to help you grow, encourage you where they can, criticize you without discouraging you, etc. It's a complex task, and some lean more towards the encouraging side than the critical side.
That's very different from the extremely Darwinian context of the professional world. A class, to some degree, is meant to PROTECT you from the harsher aspects of the professional world so you can grow and come out stronger to face the latter.
A recommendation, on the other hand, comes down to picking you out of the very large crowd looking for representation and saying, "Pick THIS person. They're better than all those other people trying to get in your door." The standards are much higher than saying you did good work that day in class.
So, basically I'd second Erin's advice, only adding there are other ways to bring the subject up - "Do you have any suggestions about getting an agent? What do you think I should have in place in terms of skill set before I do? Do you think I'm ready?" Etc.
The essential, as in many delicate human relationships one doesn't want to jeopardize, is to make your concern known without putting the other person on the spot. It's not like they can't guess what you want - most actors looking for representation would like referrals.
Bear in mind too that however the person feels about your work, there's the old "if I do it for you....". This CD may have found it's better to have a blanket rule not to do this rather than create jealousy in his or her class.
So, basically, raise the subject, but don't put the person on the spot. However works best for your particular style.