No, there is no any special low which can provide you with visa if you are not married with your fiance, even you have common children. You can come to Russia to marry and make permission for temporary residence without quotas for three years.

В РФ нет временных регистраций. За нарушение режима пребывания в РФ предусмотрено наказание в соответствии со ст. 18.8 КоАП РФ.   КоАП РФ Статья 18.8. Нарушение иностранным гражданином или лицом без гражданства правил въезда в Российскую Федерацию либо режима пребывания (проживания) в Российской Ф…

I think it might be you just have to go to recruiting agency and interview with someone who speaks english.

Dear all , i have not married a russian woman in Greece but i have with her a son , who has already 2 nationalities ( Greek -mine and mothers-Russian ) , are there any special low who can provide me with visa in order to stay with my son and my fiance?? they already live at Tiumen region.