Dear Tiago Mata,

your research deals with a terrific and stimulating topic but,
unfortunately, it's not easy to cope with it, particularly for the lack of
published sources, especially outside Poland.
In addition to the ones suggested by Michal Brzezinski, you could check also
these articles:

- BERGSON A. (1967), “Market Socialism Revisited”, Journal of Political
Economy, vol.75, no.5, pp.655-73.
- BRUS W., KOWALIK T. (1970), “L’Economie et le Socialisme selon Oskar
Lange”, Cahiers de l’Isea, vol. IV, no.1, pp.147-184.
- CHILOSI A. (1992), “Market Socialism: a Historical View and a
Retrospective Assessment”, Economic Systems, vol.16, no.1, April 1992,
pp171-185.
- CONIGLIONE F. (1993), “Scientific Philosophy and Marxism in Poland”, in
Polish Philosophy: the Lvov-Warsaw School, Rodopi, Atlanta 1993, pp.69-114
- ELLIOT J.E. (1976), “Marx and Contemporary Models of Socialist Economy”,
History of Political Economy, vol.8, no.2, pp.151-184.
- FISHER W.D. (1966), “Oskar Ryszard Lange, 1904-1965”, in Econometrica,
vol.34, no.4, (Ott. 1966), pp. 733-738.
- KALECKI M. (1966), “Oscar Lange 1904-1965”, in The Economic Journal,
vol.76, No.302 (Jun. 1966), pp.431-432.
- NOWICKI A. (1961), “L’Economie ‘Generalisée’ et la Pensée Actuelle d’Oskar
Lange”, Cahiers de l’Isea, serie G, no.11, pp. 3-177.
- ROMANIUK K. (1965), “Oskar Lange, 1904-1965”, in Review of the
International Statistical Institute, vol.34, no.2, p.294.
- SADLER C. (1977), “Pro-Soviet Polish Americans: Oskar Lange and Russia’s
Friends in the Polonia, 1941-1945”, in Polish Review, 22, no.4, pp.25-39.
- TEMKIN G. (1989), “On Economic Reforms in Socialist Countries: the Debate
on Economic Calculation under Socialism Revisited”, Communist Economies,
vol.1, no.1, pp.31-59.
- WELLISZ S. (1968), “Oskar Lange”, in International Encyclopaedia of the
Social Sciences, New York, Gale, pp. 581-584.

Secondly, you should give a look to these books:

- SADOWSKI Z. (ed.) (2005), Oskar Lange a wspolczesnosc, Warszawa:
Wydawnictwo Polskiego Towarzystwa Ekonomicznego, 2005. (it's a volume
published in occasion of Lange's centennial; the editor is Polish, but the
most part of the articles is in English)
- ASSOUS M. , LOPEZ J.M. (2010) Michal Kalecki, Palgrave Mac-Millan.

Thirdly, you should check the several series of the journal "Ekonomista".
Unfortunately the articles are in Polish, but very often there's an abstract
in English so that you can choose what eventually has to be translated.
In Europe, the journal is available at the Polish Academy of Sciences, I
think that in the U.S. you could try at the Kosciuszko Foundation, NYC.

Finally, I strongly recommend you to contact Prof. Tadeusz Kowalik (Polish
Academy of Sciences, Warsaw),  Prof. Jan Toporowski (SOAS, London) and Prof.
Anita Prazmowska (LSE).

Best Regards,
Roberto Lampa