Buying Tickets at the park

So I'm taking my kids to Disney later this week and got the bright idea to head to Orlando a day early so we could go to Epic Universe on Oct 8th. But I see online that single day passes are not available for that day or most of the week. But there's plenty of availability when booking a multi day package. I understand it could be a risk, but is it likely or not that I'll be able to get passes if I arrive to the park ticket counter that morning? Or is this a simple cash grab by Universal to get people to buy higher priced packages? Not really interested in a multi-day pass cause we've been to the other parks a few times. Fall back plan is we did get a complimentary pass to one of the Disney water parks on the 8th.