The easiest way is to, as Charlieman said, to just buy a full, complete LC630 DOS board.
The logic board used in the LC630 DOS is not "special", but rather, updated. It uses the exact same board as the LC580, which has two SIMM slots, and the Apple Internal Video Connector, which is used to provide external video out on the 580 (with a very hard to find adaptor cable), or to send video from the LC630 DOS board to the display on the LC630 DOS.
Either way, you'll still find it a lot easier to simply track down a full LC630 DOS board rather than just the bare card, not to mention that to use the card, as well as needing the card, you'll need the video adaptor, the sound card, and the gameport/LC PDS adaptor, all of which you'll only be able to get from an LC630 DOS Compatible.