I think you are currently on COBRA, if not you can get COBRA for up to 36 months.
You are eligible to continue your COBRA by an additional 18 months after the initial 18 is exhausted.
http://www.dol.gov/ebsa/faqs/faq-consumer-cobra.html
"Q14: Is a divorced spouse entitled to COBRA coverage from their former spouses' group health plan?
Under COBRA, participants, covered spouses and dependent children may continue their plan coverage for a limited time when they would otherwise lose coverage due to a particular event, such as divorce (or legal separation). A covered employee's spouse who would lose coverage due to a divorce may elect continuation coverage under the plan for a maximum of 36 months. A qualified beneficiary must notify the plan administrator of a qualifying event within 60 days after divorce or legal separation. After being notified of a divorce, the plan administrator must give notice, generally within 14 days, to the qualified beneficiary of the right to elect COBRA continuation coverage."