score:4
A few hundred or a few thousand rifles and handguns are nothing compared to the small arms issued to men by the thousands and millions during World War I and World War II. Most of the WWII weapons were not yet manufactured in 1934 but there were millions of WWI era and older weapons around in 1934.
If, for example, there were 10,000,000 each of rifles and pistols issued during WWI, and post war programs to collect those small arms were ninety percent successful, that would result in 1,000,000 each of pistols and rifles remaining in private hands after the end of WWI which was many times the numbers in the question.
And I believe that ordering pistols, rifles, and ammunition by mail order was legal and respectable in the USA and some other countries at that time, so if any Austrians got in contact with gun companies in the USA they could have ordered guns from them, though they might face problems importing those guns and might have to arrange to smuggle them into the country.
It is also a fact that there have been many wars, civil wars, revolutions, uprisings, and other conflicts in Europe in the 1920s, when various groups wanted or needed to get lots of weapons, many times the numbers mentioned in the question, and they managed to get those weapons.
Therefore, the Austrian Social Democrats were probably rather small scale customers in the European white, gray, and black arms markets of the times.
Upvote:3
Civilians in central Europe might require a license to own a gun, and possibly provide a credible explanation when they applied for the license (and/or pass a background check), but there remained countless hunters and other gun owners. These people were required to account for the weapons they held, but if there is a market, there is a black market.