There is no magic formula or index covering all participants in the campaign. Zulu War researchers who have spent years collecting data from extensive sources may publish their findings, but in the interim it is unreasonable to expect them to hand out their hard-won information on a plate. If you hire a professional to research a specific individual on your behalf e.g. at TNA, that is a different matter.
Where service records haven't survived, the outline of a regular soldier's career can be traced via avenues such as Pay Lists and Muster Rolls. The British Treasury of the 19th century operated on the assumption that everyone was trying to cheat the government: this meant that documentation relating to payment of government monies was carefully kept. British regiments at home and abroad had to send copies of their Pay Lists and Muster Rolls to the Commander-in-Chief for audit purposes. Check TNA's catalogue, also for relevant Description Books in which regiments recorded details of all men serving in the regiment - physical description, age, birthplace, trade, any former service.
Service Pension Books are under WO 117: from 1857 the entries are arranged by the registered Chelsea Pension Number correlating to that used in WO 97 when soldiers were discharged to pension.