I don't know of any nurses support groups, but some ways you can improve your skills on your own:
1. Specific journals. Journal of Psychosocial Nursing often has articles on addictions nursing. Journal of Addictions Nursing is pretty much all of it. You may be able to access either/both though your facility or local library. Or if you decide to spring for a subscription, you can write it off as a business expense (however please consult with your tax preparer/lawyer for the 100% legally correct answer).
2. CEUs. There's lot of them online...good portion are free or low cost.
3. IntNSA: International Nurses Society on Addictions. They accept LVNs as members. There is supposedly a SoCal chapter in the works...at the very least, you can find members in the area and e-mail them. Plus it includes access to the Journal of Addictions Nursing.
4. You don't necessarily need a nurse to be your mentor: ask questions of all knowledgeable staff regardless of who they are. You can learn a lot from non-licensed staff such as social workers, addictions counselors, etc. You'd also be surprised how willing addictionologist/addiction MDs are to answer your questions.
5. Every now and then, attend open recovery support group meetings (AA, NA, SMART, etc). No need to identify yourself as a nurse. You can learn a lot about addictions from hearing stories about the disease first-hand. Plus since you're not their nurse, you'll be able to listen to their stories more objectively, whereas if they are patients in your care, you may be skeptical of their intentions...and yes, that can happen to the best of us at times