The most up-to-date search site is going to be austinhomesearch.com It's in the web reference to this answer.
The realtor.com website has problems with being updated on a timely basis and can be up to 2 weeks behind, meaning that some properties that are listed as available on that site, might actually be sold. And others that are available, are often times delayed in being listed. The Austinhomesearch site is a direct feed with updates every 12 hours.
As for lofts, the definition is somewhat vague in our industry. You need to be a bit more specific as to exactly what it is you're looking for, whether or not you want a low-rise, mid-rise or high-rise building (yes, lofts can exist in even a high-rise, although that's probably not what you had in mind). If you use any of the search sites and enter a property type of "loft", you might not see what it is you expect in a true "loft" design.
You also need to consider the area of town. Being "in" downtown Austin is very different than being "nearby". And "nearby" can be much more risky, since the further outside of Austin you get, the less stable the market is for "loft" type properties, which means your long term investment is also more risky.
Since you're wanting to buy a condo, and not be sold a condo, consider checking out my profile and see if it might be a good fit.