In this paper a computationally efficient solution is proposed for the reachable sequence computation problem in the context of sub and superconservative discrete state Chemical Reaction Network (CRN) subclasses. It is shown that a minimal-length reachable state transition sequence and reaction vector sequence can be determined in polynomial time, assuming that the reachability relation holds. A constructive proof is provided in which a computational procedure is composed to find a reachable state transition sequence, provided a pair of initial and target states. In the studied subclasses of discrete state CRNs it is known that the reachability problem - as a decision problem - can be decided in polynomial time by solving a Linear Program formulated by means of the CRN state equation. Leveraging the LP relaxation, the constructed procedure formulates the computational problem of feasible sequence calculation by iteratively solving Linear Programs related to the decision problem of CRN reachability.