For J-spec cars where you can pull the VIN (not that that's common...), each makers have grade search system on their websites. Unfortunately they aren't really as comprehensive as dhill's VIN decoders, plus some of these manufacturers barely go back to even the 2000s...

Toyota - https://www.toyota.co.jp/grade/dc/top
Nissan - https://grade-search.nissan.co.jp/GRADE/search.html
Honda - https://grade.customer.honda.co.jp/apps/grade/hccg0010101/agree (have to agree to TOS first; however they're the most comprehensive out of all brands)
Subaru - http://grade-search.subaru.jp/luw/
Mazda - http://support.mazda.co.jp/grade-search/ (passenger car only)
Mitsubishi - https://inquiry.mitsubishi-motors.co.jp/reference/GradeSearch.do
Daihatsu - http://inquiry.daihatsu.co.jp/gradeweb/Default2.aspx
Suzuki - http://grade-search.suzuki.co.jp/SGRE/page/gradeSearch.html

I hope they aren't region locked...