You could try asking here:
Or faltboot.org which is focused on folding kayaks.
There are bike transport services at least along popular stretches (like Passau - Wien Donauradweg) - and kayak as well:
(the first I found, there are perhaps more)
(90 Euros a kayak for a week, shuttle something like 50 Eurocent/km) - GST should be included. ;-)
I guess it depends a lot on which part you want to paddle.
4-paddlers.com used to be an informative site - but it's not working at least at the moment.
Last edited by Kokanee75; 11-12-2018 at 10:37 AM.