Long or Short action, Staggerfeed model?

You have a ton of options.
For replacement: Midway, Brownells, GunShack, the several vendors we have on this site will also likely be a help for you. Or you can become a paid member, and look through the classifieds.

For a conversion: There are a few folks that can in-let the stock and use detachable mags. Some systems us the AI mags. Can't say the name off the top of my head, but just use the search function and you'll find it.