So if you could find the app outside of the Google play store, would you be able to store it on the external sd. Amazon marketplace for instance. Obviously not all apps are available from amazon, but a number of the free ones are. Would this be a viable workaround?
No. Regardless of where they come from, all apps will install to the internal memory unless you're rooted and using something like Directory Bind like Batman8 and others mentioned.
And Batman8 is entirely correct. This is the direction that Android is moving in. Motorola was doing it on Gingerbread, and I've yet to see an ICS device that natively allows the installation of apps to the SD card. This was a choice made by Google for a variety of reasons (with stability being one of the major ones). Luckily, for those who need the expandable storage for applications, there are ways to work around it if you're rooted.