Is there a substitute for “him/her” which is commonly used in formal texts?

Yes, there is. There is a tendency nowadays among native speakers to replace “him/her” with the plural pronouns “they”, “their”, and `them”.
*If anyone is interested in going, they can get in touch with Bala. *If anyone calls, tell them I am not in town.
Grammar pundits would argue that both these sentences are wrong because “anyone” is singular and therefore should be followed by “him/her” — it should not be followed by the plural “they” or “them”. Native speakers of English feel that the use of “him/her” makes the construction look clumsy and therefore should be avoided.
Source:  ‘Know Your English’ Series – The Hindu Daily, August 29 , 2005.