Bhante Sitalo,

> It seems that mentioning about Seven Visuddhis and Vipassana is
> already in the Tipitaka as it is in translation of Rathaviniita
> Sutta clearly stated.

No, there's no mention of 'vipassana' in the Pali text of Rathavinita sutta.

For a better translation see:
http://www.accesstoinsight.org/canon/majjhima/mn24.html

> Many around me had said that the term
> Vipassana is really found in Tipitaka, but mainly could be found in
> Atthaakathas etc.,(commentaries and sub-commentaries). So here it
> is, found in Majjhimanikaaya, Muulapa.n.naasa Paa.li, Rathaviniita
> Sutta. Where else could it be found?

See
http://www.accesstoinsight.org/index-subject.html#vipassana
http://dhamma.ru/canon/an4-94.htm
http://dhamma.ru/canon/an4-170.htm
http://dhamma.ru/canon/an2-29.htm

With reverence, Dmytro