There's also this open source design: https://gitlab.com/doragasu/sms-sl2map https://gitlab.com/doragasu/sms-sl2map It doesn't handle all the features of the s

There's also this open source design: https://gitlab.com/doragasu/sms-sl2map https://gitlab.com/doragasu/sms-sl2map It doesn't handle all the features of the standard mapper so not compatible with all games, but it's designed to be cheap to manufacture. Unfortunately I don't think anyone is selling these so you'll need to take the files to a PCBA house (or get bare PCBs manufactured and do assembly yourself)