To find a family's notarial records, if any survive, requires knowing the name of their notaire. This is because the documents are catalogued by the name of the notaire and the étude, in the Archives départementales, within series E. Normally, each archives will maintain a chronological list of the names of the notaires working in each area. If you know where your ancestors lived, you can then find which notaire was working in that area at that time. Then, it is just a matter of leafing through that notaire's documents for that time period.
Notarial records had to be registered. There are numerous registres du Contrôle des actes is in the Archives départementales. Unfortunately, they are not all in the same series. If the notaire is not known, but the date, place and family involved are known, it may be possible to locate the reference to the document in the registre. It seems that, across the country for marriage contracts, the registre (in series Q) is better for some years than for others: 1793-1850 is pretty good; 1850-1865 is said to be useless, but at least having tables - chronological indices; 1865-1904, generally also useless, without even having indices. (One begins to have the impression that notaires are a recalcitrant bunch.)
If there was a marriage contract, it should be mentioned, along with the notaire's name, in any acte de mariage after 1850. If the name of the notaire is not mentioned, it's off to those tricky registres. If it still cannot be found, it may be possible to find the dowry payment documents - les quittances de dot - or a will later, with a copy of the marriage contract attached.
Finding a will is aided by the Bureau de Successions, an office where deaths were reported and logged. In many of the log books it will be stated whether the deceased left a will, along with the name of the notaire involved.
Finding notarial records is not terribly difficult; finding all such records for a family can be exhausting, but well worth the effort.
2010 Anne Morddel