http://www.r4isdhc.hk/download_white_new2014/index.htmI'll keep mine in the crappy condition it is(scratches, broken plastic, and cartridge coming apart because I took it apart, and it just won't stick together, so it's taped together)
http://www.r4isdhc.hk/download_white_new2013/index.htm
These carts have the same file structure as the one you mentioned. _rpg folder, with r4_sd.dldi etc inside it. It's more likely one of those. Hopefully it's not one of the older models on the site, as the download links for them are all dead.
Those carts are also white and they have notches on the sides the same way your bootleg cart does.










