welcome to the Forum....do you know what the crack was cause by ( from)??? if it split from the locating pin hole,or through the "grain " layout, may just be a factory 'defect' ... a picture would help, or contact Ruger, maybe send the grip panel back to them........if from "misuse" normal wear and tear or improper removal ( prying them off with a screw driver or a chisel...) then you may have to try and locate another pair on such as e-bay or any gun selling site that has accessories OR even post an 'ad' here on the classifieds of this Forum.........
Welcome to the Forum.
First, you didn't say if it's an Old Model, or a New Model. If it's a NM, any good gun shop can order a set of new grips. If it's an OM, and you want a set of correct grips,, you'll probably have to place a WTB ad here in the classifieds.