Yes, there are lots of lawyers who specialize in medical marijuana law. I am one and here is my take on your situation: Registering as a narcotic offender does not interfere with your medical marijuana use or subject you to search. However, being on probation with a search clause (which you probably have) does subject you to search at any time, for any reason. The law says that you can still use medical marijuana during Prop. 36 probation, but the law is unsettled about what kind of power a judge has to limit this or violate you for it. There is a good case that says that a judge can't violate your probation for using medical marijuana, unless your use of marijuana is somehow related to your criminal history or the likelihood of future criminality. There are two bad cases now which give the court broader power to prevent you from using medical marijuana on probation. The issue needs to be resolved by the California Supreme Court, which may not happen for some time, if at all.
This leaves you with two choices: 1. Be upfront about it and take the chance that they will tell you not to do it. 2. Keep smoking and, when you get a dirty urine for marijuana, argue that the court should not violate your probation because you have a medical marijuana recommendation. If the court does violate you, appeal it. You usually don't get kicked out of Prop. 36 until your third violation.
I wouldn't take option number two, unless you have a valid and up to date medical marijuana recommendation and your criminal history doesn't reflect things that are related to your use (not possession) of marijuana, such as driving while high on marijuana, disorderly conduct while high on marijuana, etc. or diverting medical marijuana for non-medical purposes.
You should talk about this with your attorney (public defender or otherwise). Many criminal defense lawyers (and judges) are ignorant about the caselaw around medical marijuana. I would tell your attorney to read Tilekooh and Beaty (the good cases) and Moret and Brooks (the bad cases) before rejecting your use of medical marijuana out of hand.
I do not know how your county's probation department will handle this. I can only tell you that in my area you simply have to let the probation department know about your license. Even though you are on Prop 36 that does not change the medical marijuana law. You can still have a license. So be up front with probation about this and see what they tell you.
I usually tell my clients to stop smokiing and get rid of the card. Ultimately it will get you into more trouble than it is worth.
Do your probation terms prohibit you from using medical marijuana? Around here many of the judges are creating terms of probation requiring that you abstain from all use of marijuana even with a medical recommendation.