Ok, so that's one full step below drop D...
You can use a medium -gauge or a light-gauge 5-string set and use those (Warwick's is 130, 100, 80, 60, 40) this way you'll get a 130 for the C, which should make it nice and tight, and then the others should be tight enough as well and give you the equivalent of a heavy-gauge set in standard tuning...