DISA is a freely accessible online scholarly resource focusing on the socio-political history of South Africa, particularly the struggle for freedom during the period from 1950 to the first democratic elections in 1994.
A search for 'The State versus Nelson Mandela' yields the following scanned documents:
Bruno Mtolo's extract of evidence (vol. 15 and vol. 16), Walter Sisulu's extract of evidence (vol. 20), Ahmed Kathrada's extract of evidence (vol. 24), Raymond Mhlaba's extract of evidence (vol. 25), Lionel Bernstein's extract of evidence (vol. 26), Govan Mbeki's extract of evidence (vol. 28), judgement, judge's remarks when passing sentence. These documents were selected and scanned from the collection at Historical Papers, University of Witwatersrand (AD1844).
A search for 'Rivonia Trial' yields a poster (linked from SAHA Poster Collection entry) and an extract from the Rivonia Trial Statement made by Nelson Mandela which appeared in the journal Dawn (Volume 7 Number 6 June 1983 page 20). There are other articles too which make mention of the significance of the Trial in passing, mostly from the African Communist magazine.