Not sure why you'd want it? What would it offer that the 3.5 one doesn't?
Actually, there are several things in the 3.0 SRD that you won't find in its 3.5 equivalent. It's a pretty motley collection, and a lot of it is stuff that 3.5 saw fit to excise, but not all of it, including:
- Psionic combat (e.g. attack and defense modes).
- Certain spells that 3.5 eliminated or broke up (e.g. emotion).
- A section on the problems with bringing druid/ranger animal companions into urban areas.
- The rule (downgraded to an optional rule in 3.5) for, when an attack against a creature with cover fails, potentially damaging whatever's granting them cover.
That's in addition to various other 3.0-isms which someone might still be interested in for a variant d20-based game, such as the greater gradations of concealment, skills such as Intuit Direction, having feats like Ambidexterity, etc.