Additional postings for downloads I haven't been able to track down yet. Might take a bit of research.
Really not sure which of these are actual gunka but Discogs brings up a lot of results
>http://www.discogs.com/search/?q=%E8%BB%8D%E6%AD%8CJapanese / buyfag / frantic Googling:
Basically there are some unpublished works from '95 in like cassettes that are hard to get or something like that.
>http://search.rakuten.co.jp/search/mall/%E8%BB%8D%E6%AD%8C/-/?scid=af_pc_etcThis has good information about gunka and also provides titles of more buyfag materials as well as links. Seems to translate okay with Google Translate.
>http://gunka.sakura.ne.jp/gunkacd.htmHere's a potential lead with a set of downloads called 大日本帝國軍歌大全集 (Google: Dai Nippon Teikoku martial music Daizenshu). It has download links which do not work.], though I was able to get the first one from the Way Back Machine archive; the others, no.
>http://japanfirst.asianfreeforum.com/t330-topic軍歌大全集 (Google: Martial music Complete Works)
This appears to be a buyfag collection. I found an archived thread from /jp/ which linked to rapidshares which unfortunately 404'd (circa 2008 so expected).
>https://warosu.org/jp/thread/1675149#p1675257>http://gunka.sakura.ne.jp/review/gunkadaizenshu.htmNow that being said, 大日本帝國軍歌大全集 and 軍歌大全集 seem to be quite similar; one just attaches Imperial Japanese Army to the front. I'm inclined to think the collection on Japan First is a truncated version of the one listed on Sakura. Really I can't tell though since it's hard to compare the file names while not speaking the language.
Cheers. Hopefully someone can find an illusive final archive for us to enjoy. Thought I'd contribute to this growing board in a way which will entertain for quite some time.