Birth Father, preparing to reunite with children

I am the Birth Father of a daughter and son, currently ages 17 & 15. Due to complications relating to a Bipolar episode, I was shut out from all contact with my children by the birth mother (wife at the time) when they were 3 and newborn. 5 years later, their stepfather requested adoption, which I consented to after a long and painful deliberation. To date, I have respected their desire for no contact while the children were growing up. I believe I know where the children live in California and how to contact them. I have no reason to believe that the birth mother would support any contact with herself or support my contact with the children. It's been ~10 years now. I have since been re-married, have a 10-year-old son, and become stable. I am preparing to reunite, initially with my daughter when she turns 18 in 2018, and later my son. Can anyone recommend a support group, etc. for birth fathers seeking to reunite with their children? Anyone that could point me in the right direction would be much appreciated. Many Thanks, Terry Musser