(a) most of the major manufacturers will provide such software to their customers
(b) there are commercial providers of such services who have done the work and will provide RTOW tables for clients at a dollar (or many)
(c) you could do the thing the long way and start with a flight manual, do the regressions or set up lookup tables (according to preference), and generate your own software .. nothing too difficult with this but be prepared for some investment in time ... not to mention the odd numerical analysis problem in achieving appropriate levels of accuracy ...