I don't use sand paper, but instead use an exo-terra rubber mat that is textured with rocks (no loose substrate, but gives that appearance). This is much courser than reptile carpet or tile, though not so much that I think it causes any discomfort.
Dragons can also wear down their claws on climbing branches if you provide them one.
Otherwise, you can trim their nails yourself; it's not a big deal. We just got our dragon last week, and as an adult he didn't mind or even notice at all when I trimmed his nails. You just clip the lone black tip that is separate from the clear bit. It doesn't hurt them at all and keeps that needle tip from digging into you!