Was this the wood stock, or synthetic ? If synthetic, I am not surprised. I found out the hard way that the standard Ruger synthetic stock is NOT fibre- reinforced... and thus rather fragile. I had a 77 mark II in .243.... and the standard stock was garbage. Unfortunate, because I thought highly of the rest of the rifle. Once re-stocked, it was a very good rifle.
As to replacement stocks, there are many brands available. Mcmillan (high-end synthetics, but probably the best), Bell and Carlson (also very good).... and many others. Most of the synthetic after-market stocks are MOSTLY drop-in...(some SMALL amount of fitting might be required, in some cases)....bedding the action might be important, again in SOME cases.... other times, not needed. It varies. If you wish to have a wood stock, then final fitting is usually required - and bedding the action almost always is needed for best results.
There are many different sources for replacement stocks.... Cabela's and other such companies.... Mcmillan you get directly from the manufacturer. Do a search for aftermarket stocks - you will find a plethora of sources.