From the wiki, the recommended drives to rip Dreamcast GD-ROMs are:

Samsung TSSTCorp models:
SH-D163A aka TS-H353A
SH-D162C aka TS-H352C

I'm having trouble finding these online. Sometimes I see one labeled as an HP or Dell with the same model number. Would that still count?

From what I've seen online, a majority (or maybe all?) of these drives were OEM drives for various manufacturers. If you see one that is the correct model number, but is an HP or Dell OEM, it should be fine to use. However, make sure you read the whole model number. Some OEMs will say something like TS-H353 Rev A in one spot, making it sound like an H353A drive, but then, in another spot, it will explicitly say TS-H353B. The rev number is not part of the model number, so the example drive would be a TS-H353B drive, not a TS-H353A drive.

I saw a TS-H353A on eBay a few days ago, although it recently sold.
I had no problem finding a TS-H352C on eBay and bought one for $11 shipped last week.

BW-16D1HT | PX-W4824TU | PX-W5224A | PX-760A | PX-712A | Plextor Premium | Pioneer 209DBK | TS-H352C | TS-H353A | Wii