They basically haven't any aviation industry left. Lohner went back to manufacturing trams, Oeffag started making car bodies for Austro-Daimler, and Phönix simply dissapeared. The designers and engineers left for other countries, so even brain power wasn't available. WKF was bought by Österreichische Waffenfabriks-Gesellschaft and was too used for vehicle subasembly.
Other than the Peace treaty prohibiting manufacturing military aircraft, Austria was also badly hit by the postwar economical depresion, so even companies who tried to shift to civilian aviation couldn't survive, especially when there was so much civilianised military aircraft the various airlines could use. Altough I don't even know any that tried it.
The only companies I found that existed during the 1920s were Flugzeugbau Hopfner and Ramor Flugzeugwerke, both making only few prototypes in the early 1930s. They simply lost the touch with the technology and progres, lost manpower, and even after the treaties weren't strongly enforced, the competition from other countries was too strong so any new company couldn't even emerge without massive backing or without finding some very specific niche.
Thus Austria haven't any aicraft industry during the 1930s, except for few tiny companies like Pinsch, who made few German Tigerschwalbes, or Wiener Neustädter Flugzeugwerke, which actually finished the last Hopfner, the HV-15, and made several sports types.
