Numbers of trials, convictions, etc. at Batavia & Makassar are accessible, I am pretty sure. I probably have all of that, actually. Let me dig through my stuff when I get a spare minute---I will be happy to help you.
You just can't access the actual trial transcripts. Very VERY VVEERRYY disappointing and frustrating! (A profoundly serious loss to PacWar historians, and IMO there can be no legitimate reasons for sealing those records...other than $$$)
I don't know whether the archive material is really still under key as Felix says it is, BUT I recently discovered a book with over 600 pages which is entirely dedicated to the Dutch prosecution of Japanese war criminals in the Dutch East Indies after World War II.
L.F. Groot: "Berechting Japanse oorlogsmisdadigers in Nederlands-Indie, 1946-1949: Temporaire Krijgsraad Batavia, Den Haag-'s-Hertogenbosch: Art & Research 1990.
Here is a short summary of the book:
GROOT, L.F. DE, Berechting Japanse Oorlogsmisdadigers in Nederlands-Indië 1946-1949. Temporaire Krijgsraad Batavia. [AUTHOR'S PROOF COPY; Eerste en enige druk in machineschrift/First and onlyTypo script edition]. Den Haag-'s-Hertogenbosch The Author/Art & Research (TYP.), 1990 Small Stout 4°., original printed wrappers. (v), 622pp. 9 black/white illustrations after drawings captioned in japanese with dutch translations, illustrating the story of two Indo-European boys (Dan Droop and Kain), arrested and interrogated after setting fire to the Canteen of "Soekarella" members at Gombong, Large fold. map of Java, 1:500.000 (reproduced from:"Schoolatlas der Geheele Aarde", 32nd. dedition, 1929), large fold. map with extensive legenda of Siam-Burma railroad-track, full-page sketch-map illustrating boundaries of the Japanese expansion, tables in text, 1, 3pp., diagramme illustrating names, ranks, sentences requisited and passed to foremost Japanese defendants, including Kenpeitai members. Extensive appendices at end of volume II, illustrating names of all 356 japanese defendants including army registration numbers and sentences passed, name-list of all filed 986 defendants brought to trial (432 sentences passed), registers compiled by Th. J. Van Houten assisted by M.P.C. Kuunders, table of contents. AUTHOR'S PROOF COPY WITH CORRECTIONS IN MS., and 10 A-4 sized printed leaves with calculations and estimations concerning its publication loosely inserted.
AUTHOR'S PROOF COPY with marginal ms. annotations and corrections, of this Massive and very detailed report of the trials against Japanese war-criminals (Including Kenpeitai-members) brought before the temporary Court Martial, under author's presidency, Batavia 1946-1949. Including extensive name-lists, ranks, military registration numers, sentences requisited and passed, background information on the Court's legal fundament, general remarks in trying war-criminals in dutch colonial Indonesia, special attention is paid to Defendants as Nozaki, Kawabe, Nakata, Suzuki Ottojiro, General-Major Yamamoto Moichiro c.s., Imamura Hitoshi, Okazaki Seisaburo, the Semaring case of forced Prostitution and the Batavia Kenpeitai section. AUSTHOR'S PROOF COPY IN ONE VOLUME with his marginal and textual corrections and annotations in Ms. in ink. Good copy. Rare. (somewhat dog-eared, vertical tear to top of front outer joint skilfully restored with clearview acidfree tape).
And finally the link to the book. Just don't look at the price and you will be fine.