Jay,
You can buy a new set of blades from GSC. It might be your least expensive option, though I don't really know their current pricing.

If you have a 3:1 gear ratio on the C box 582, IVO only recommends the two blade medium. That's what I'm running (70") and it works well, but it's a pretty high inertia prop which resulted in extremely rough idle. I eventually installed a RK400 clutch to resolve this issue.

Other people go ahead and run the three blade ultralight and are happy with it. It's just not recommended by the manufacturer.