Most quality scope makers offer a 30mm series of scopes. The defacto standard is 1" (25.4 mm). To list a "few" of the available 30mm scopes.
Leupold - Several models, some Mk4's, some others.
Burris - Black Diamond, Euro Diamond
Nikon - Tactical Series, Monarch Gold
Bushnell (B&L) - Elite 3200 Euro 3-9x50mm
Swarovski, Zeiss, US Optics, Super Sniper, & springfield armory all offer 30mm also.
Most high end scope makers have some sort of 30mm tube scope
MEL