Those are both 1950s/1960s shows... I'm not sure what railroad equipment any of them had back then, but the major studios, specifically MGM and 20th Century Fox, both had huge backlots where frankly they could have fit some RR equipment if needed. Warner's still has the Warner's Ranch, but I'm not covinced that's big enough.

That being said, during my time in television (many decades later) all railroad shooting was done practical (meaning that we would go out to where a train was). In the 1980s, 1990s, and 2000s, I wasn't aware of any studio owned railroad equipment (unless you include the fact that some studios also owned themeparks, but those were not props).