Hi fren.
The nearest railway station from Kathmandu is raxaul but the biggest and most convenient is gorakhpur. In fact most of Nepali people or travellers coming from Nepal use gorakhpur as transit point
There are direct trains available from gorakhpur to raipur.
Now going for raipur, you don't even need to go to gorakhpur. The nautanwa/ntv station,...
more... which is situated at around 10 km from bhairahawa boarder, has a direct train to raipur. This train goes via gorakhpur.
If you want to reach gorakhpur anyway, there are frequent bus,sumo and shared taxis available. It takes you about 2-3 hours.
Please free to ask in case of any confusion.