The very first production model DVD hardware didn't even start showing up until 1997. That was the end of the 68k era, and very close to the end of the Beige PowerPC era, certainly the end of the pre-G3 era. No DVD drive was ever specifically marketed for 68k Macs, as nobody thought there'd be a market for such a thing. The Mac OS didn't support DVD drives until OS 8.1 showed up, from memory the first Mac to come configurable from Apple with a DVD drive was the Wallstreet, and they didn't really get serious about it until 1999, when the B&W G3, and later on the Lombard G3, and slot load iMacs showed up.
That said - there are SCSI DVD-ROM and DVD-RAM drives available, and if you can find System 7, 68k compatible drivers there's no reason as to why you shouldn't be able to get a SCSI DVD drive to work on a 68k.