Here is an [http://www.ebay.com/bhp/vw-beetle-seat-belt|ebay] link to the belt part, but there are lots of other parts in the list. It looks like most of them are either passenger or rear seat belts, or a combination thereof. [http://www.ebay.com/itm/1998-VW-BEETLE-TDI-LH-DRIVER-SIDE-FRONT-SEAT-BELT-ASSEMBLY-95012-W-RETRACTOR-EUC-/111470714422?hash=item19f42c1e36:g:4P0AAOSwEK9UIhJN|This] might be just what you need, though.
[https://www.wescoperformance.com/seat-belt-install-3-point-retract.html|Here]'s an installation guide.
You got this!