after having the tyres pulled off the rims today, to go to be powdercoated, i noticed they have "CRIMSON INC." and "ASAHITEC" written on the inside lip.
crimson inc. - http://www.crimson-inc.co.jp/ - seem to make sparco rims, but i couldn't see mine on there, and i can't read japanese, nor could i email them
asahi tec - http://www.asahitec.co.jp/english/ - seem to be involved in making forged aluminium rims, which these are, but i couldn't see sparco rims on there either.