The digitizers are easily found and should be under$20 (see Marty's link). The screens themselves are pretty much impossible to find. You'll have to go through RCA for an official replacement part. go to shop.rcaav.com, but you will not find it listed anywhere. Click get support in the corner and you'll have to order through the support person. They are about $40-$45.
I had the same problem, but we are currently trying to decide whether it is worth it to us to repair. With tablet prices coming down, we are strongly considering just replacing it with something new.