For the sake of Parnasá, is a person Shomer Shabat, in dire need of work, be allowed to work on Shabat. Living a country where most businesses are open on Shabat and little opportunities to obtain a job, is there any dispensation in the Halacha, that allows a person with wife and children to accept a job that obliges him to work on Shabat?.

There is no dispension in the Halacha. This is a very difficult trial - even so you are oblidged to to keep Shabbat to the extreme. One should try and live in an area that does not offer such complications. Hashem will send you blessing and help. Rabbi Ro'i Margalit