You can use generic rolls. They must be single ply thermal paper with the following dimensions:
Type: thermal receipt paper
Width: 3.13" +/- 0.02" (79.5mm +/- 0.5mm)
Core: unglued
Maximum roll diameter: 3.27" (83mm)
This applies to all of Wasp's receipt printer models, including:
RP300H
RP330
RP200
WRP8055
WTP100