There is no specific fund specified in the act from which gratuity is paid. Depending on the size of the organization, you need to create your own fund. You need to sit and work this out based on your conditions. If the business is large (and profit margins are good), and the number of employees working more than 5 years is low, you may not need a fund as the business can afford to pay gratuity to the few who leave. However, in order to ensure smooth cash flow and avoid disruption in case a large number leave at the same time, companies prefer to set aside some money for this. Ask your finance team how they can do it.
Remember that anyone dying while in employment is entitled to gratuity even if they have not completed 5 years. Further, there is a provision in the act for compulsory insurance, which I think is for larger companies. You can get in touch with LIC or one of the private insurance companies and check out their schemes. You get some tax benefits also for putting money into these schemes.
In creating your fund, remember that gratuity is based on the last drawn salary. So, you need to reset the amount upwards every year.
Regards.