X2 capacitor alternative component or circuit?
Replacing an X2 capacitor with a non-safety type of capacitor is not recommended. The extra ruggedness built into them are needed when you're dealing with the unpredictable nature of input AC. Furthermore, if you put a non-recognized capacitor in there, plug the monitor in and your house burns down, good luck getting any insurance money.

Failures of X2 capacitors are extremely rare in my experience (when used as an input line filter) - I've been working in the switching power supply industry for more than 15 years and I cannot say I've ever seen one. If you cannot find the exact part, a less dangerous substitution would be another X2 capacitor with the same ratings from a different manufacturer (Panasonic, Elna, Wima, Kemet, etc.)