New stock...
Scribe--You wanted a synthetic stock; can't help you there. If you can accept laminated wood instead, I urge you to check out Boyd's Stocks. For the k98 they have a bunch. Laminated wood is a trifle heavier; almost as impervious to moisture & humidity changes.
If you get an "unfinished" one (just means not finish-sanded nor varnished--all the inletting is finished) it's easy to glass bed yr rifle before doing the finish-sanding and varnishing. Plus if you want to make minor modifications to the stock's general shape, that works too.
The Boyd's 'phone people are used to talking newbies through the process.
Boyd's, or Midway, sells glass bedding kits. You can use local sandpaper and spray-can varnish.
However you go on this project, please keep us updated. Oh, and pix are always nice! Good luck!
ETA: One more thought--You wanted a drop-in stock, but with military rifles, there are always so many minor differences in dimensions that (a) if it were truly drop-in for all examples of a particular model, it'd have to be very sloppy for most of them, and therefore (b) there is almost always a little fitting to do with a fine file, Dremel tool, sandpaper-on-a-stick, or such. So you don't really want complete drop-in.