Hey guys! Welcome to our community It’s great having newcomers that want to participate in the forum and contribute as well. This app and community are unmatched, IMHO. I can provide you with the link to the plugin from the Audulus 3 main site. It is worth noting that without having the actual A3 application, the Audio Unit upgrade will do you no good. Anyway, here is the link to A3 AU for Mac.
As far as your concerns about purchase, yes, version 4 looms on the horizon, and it will have a bunch of awesome new features, but none of us are aware of an exact release date; the release could be a month out, or maybe 6 months. This whole application is built and maintained by one awesome developer, @Taylor. He is working very hard to get A4 out for us, but he doesn’t like the stress of deadlines, as they can hinder quality, and he wants the new version to be all that we have been excited for, and nothing less. It will definitely be worth the wait, there is no question about it.
As to whether or not you should buy A3 now or wait - that is really on you to decide. If you are like me, you will end up buying A3 and be happy to have an upgraded awesome version now. I just don’t like waiting and not knowing since release dates can vary so wildly depending on many unknown factors.
Also, since Audulus, as an app is an independent dev’s labor of love for modular synthesis, I would argue that it is an awesome thing if you end up buying both (if you have the financial means to do so) just for the principle of supporting small business to do great things that corporate giants have tried to imitate, but can’t duplicate. Anyway, I hope this helps you both with your inquiry, and we hope to see you around the forum synth-nerding out with us!