The only published orchestral work of his I have so far found is a march, but I will look further … also, not every library is listed online, and it also helps to remember which major ones that are, aren’t included by Worldcat.
If there are recent good books or dissertations about his life and music these would be better sources than the approaches I usually take. Of course, they each require so much effort to write that not every composer can be the subject of one
As to your 2nd question, -if- these works were published by 1930 or so and -if- we can somehow acquire copies to scan or what have you then sometime in the next few years, US-public domain copies could be available here…
Is the Japan Suite an orchestration of In Japan for piano do you suppose?
Also:
there is a violin concerto- with orchestra?- by Szántó listed briefly in “ The Violin Concerto Through a Period of Nearly 300 Years Covering about 3300 Concertos, with Brief Biographies of 1000 Composers” and which would have to be included in your list