It's perfectly appropriate to have small khachkars in the home. Finding them can be a bit tricky, though. Usually they are hand carved from wood and are small enough that someone could put them on a table or desk. Most come from Armenia, so supplies are not consistent. A store may have a few one month, and then have none for a while. So I would call around first to see if a store has them, and ask about prices.
You could try the Armenian Diocese bookstore in Burbank. Call ahead before you go, though, as they are not always open. Also, there is Berj Bookstore, and Abril Books in Glendale. St. Vartan Bookstore in New York may have some. I would e-mail them about it if you can't find them elsewhere.