Hi Erin,
The OeBB IC bus can be booked at the same place and in the same way as any of their trains, at oebb.at.
But I’d advise against doing so, for the following reasons:
- At €10 to reserve, taking this bus with a pass is only €4.90 cheaper than pre-booking a standalone ticket. If you have a flexi-pass and plan on doing only this journey, it is categorically not worth spending a travel day on.
- There are trains that link these two places. Either take the direct 09:56/15:52 Railjet (€13 in 2nd class, €18 in 1st, €30 in Business 1st), or take a regional train to Udine and then the 17:22 Micotra train to Villach (neither require reservation).
You generally can assume the schedule you see on the Interrail app is correct, but if you’re concerned about any particularly important connections you can always compare it to the timetable on the website of the particular train provider, or to the timetable at bahn.com.
Trains marked “Details unavailable” in the app almost always don’t require reservation, but let me know if there’s any particular one you’re wondering about and I might be able to confirm this for you.
Best of luck with your itinerary! :-)