Parts are currently available in 12mm, 16mm and 24mm wide, 4mm pitch carrier tape. Overall price will obviously depend on part size and mix, total volume, and most significantly, how many SMT blocks are actually required to provide the necessary shielding.
Longer lengths are under development.
While this is technically feasible, it defeats the purpose of making 'standard' parts, which can be used as building blocks to form a complete design. Curved features can be sufficiently approximated by straight segments, especially if considered early in the PCB layout. While the optimal gasket design would be continuous, gaps do not necessarily mean significantly degraded performance. This will depend greatly upon system architecture and frequency. This is because shielding is purely a z-axis phenomenon, and is why discretely placed BeCu contact 'spring fingers' can work on some handset designs.