I would try Shotgun News, or Gunlist. It may be cheaper to find a used gun (either previously sporterized or a surplus 98)to start with. I have a 1933 manufactured Oberndorf Mauser, lightly sporterized by my dad (Williams sights, Herters stock, dropped bolt handle) that I have often considered completing. Be aware that by the time you are done doing a real build- new barrel, drill and tap, safety conversion, scope mounts and quality scope, and stock,bolt bending, replacement trigger,etc. etc. you will easily be double what a fine new productioin rifle would cost. Even then, other than having a true custom gun, value wise you will not be ahead, and it probably still wont be on a par weight wise with most new production rifles.