Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
We do not know any special Du’a that the person should say after prayer if they want their daughters to get married. But one should supplicate with what fulfills the objective. One should also choose the times where Du’a is proved to be accepted and responded to, like after prescribed prayers.
One should also spare no effort in using legal ways that help in this, such as:
1) Informing some good and pious girls to look for pious young men who would be good suitors for these girls.
2) You may also present your daughters to any man whose character and religion you are satisfied with. There is nothing bad in that. Umar Ibn Al Khattab (Radiya Allahu Anhu) presented his daughter Hafsa (Radiya Allahu Anha) to Abu Bakr (Radiya Allahu Anhu) then to Uthman (Radiya Allahu Anhu).
We ask Allah, The Great, The Lord of The Great Throne, to ease the matters of your daughters and give them good pious husbands.
Allah knows best.