Once you have found the stock you want, its pretty easy. I have done it a couple of times, but the stock options are limited. Also, You can send any centerfeed stock that is made for a blind mag to a few of the site sponser guys (SSS, SinArms, and Northland I think) and they can inlet the bottom for a DBM setup.
To do the actual magazine conversion, all you need is the bottom metal or some may call it the frame, and the Cap for the bottom of your magazine box. The magazine box you currently have in your blind mag centerfeed just snaps onto the Piece of metal and creates a complete DBM. Then you bolt the Bottom metal or frame onto your new stock, and that's it. I know for sure you can purchase what you need from SharpShooter Supply, and possibly from others on here. THe parts are also available in the classifieds section quite frequently if you keep an eye out.