Hey @Elisabeth Lernhardt! Lots of similar platforms out there, try Redfin, Realtor, Trulia for a similar experience. Auction.com and Homepath.com have foreclosure sales. Or even ask a local Realtor to get set up on an MLS search and have properties sent to you that match your criteria. Best of luck!
Realtor.com sources from MLSes nationwide as both the MLSes and Realtor are part of NAR. If it's not in Realtor it's either off-market or the dummy that listed it put it into the wrong category. If you can get to Realtor you basically have just bypassed any agents to get to the MLS.
What an agent can do is employ some special knowledge and familiarity with quirks and dirty secrets of their local MLS, such as how less savvy listing agents drop their listings into the wrong category and subcategory making it not show up on search sites like Realtor. Agents often also have a short list of off-market deals for their valued and exclusive-signed clients which won't come from any public search engine. Agents will also have market knowledge of their area and a public search engine will leave that research up to you.
I was frustrated with Zillow too. It seems great to look up properties, but it's difficult to go into details about them and analyze comps. I found Redfin to be much more helpful. You can get a map of similar properties and it's much easier to navigate. I just finished analyzing my first 100 properties (suggested by Brandon Turner on the podcast). I usually start with Zillow to identify them, then switch to Redfin to fill out the details on my spreadsheet when analyzing them.