@vtrn_raptor I don't think there's a single 'How To' thread for making a brake caliper adaptor bracket, as I was going to do it myself, but instead I have decided to take a different route. However there is quite a bit of info around on upgrading the DT's brakes. If you read this topic on here, that has some great info and links;
http://www.dt125r.co.uk/topic/189/brake-upgrades
However if you are looking to do a full supermoto conversion you may find it easier to use these donor parts, as that would give you less complications and it would pretty much be a straight bolt on affair;
http://www.dt125r.co.uk/topic/207/how-to-supermoto-a-dt-using-donor-parts-from-other-yammy-s