A cooperative agreement may authorize the board of directors to purchase excess or catastrophic insurance on behalf of the joint insurance arrangement. The cost of the insurance shall be apportioned in the manner specified in the joint insurance agreement. The board may purchase insurance under this section only from an insurer authorized to do business in the state, except that an arrangement formed by municipalities or school districts may purchase insurance under this section from a risk-sharing pool established by a national association of similar entities if the risk-sharing pool meets the qualifications for an unauthorized insurer under AS 21.34.040(b) and (d) and 21.34.220 and has capital and policyholders surplus in an amount at least as great as would be required if the association were a domestic multiple line insurer. An arrangement may purchase insurance under this section for property and liability risks from unauthorized insurers allowed for use by licensed Alaska surplus lines brokers.