Looking for tiles as well as floorplans will expand your options. Tiles are great (and more common) for some smaller areas or where you want more detail, while floorplans can be more or less detailed depending on the scale.
An easy source is for-pay PDFs of tiles and floorplans. RPGNow hosts a lot of PDF publishers who specialise in floor tiles (for example, the e-Future tiles line were the first that came up when I searched) and there are tonnes of unmarked floor plans available. Similarly, searching for "tile modern" turns up boats, diners, office buildings, subway… For-pay PDFs vary in price and quality, but there is a lot of variety out there and everyone has samples to help you determine if you like their work. This is probably the most reliable "better way". Floorplan PDFs tend to be a bit cheaper than tiles simply because there isn't as much a market for them, not being immediately useful for battle-map styles of games.
Another source is The Cartographers' Guild, a forum/community of map-makers. Searching for "science fiction" or "sci fi" and "tile" (sorry, no direct link to the search URL due to the way the forum software works) yielded me a bunch of ship tiles, while "modern floorplan" turned up a sawmill, chapel, office buildings, and a bowling alley. It looks like requests are sometimes taken, though of course that's going to depend on the people involved. (NB that you have to register as a member to view or download image attachments.)
There are also a few old and current board games that tend to attract fan-made tiles. For a science fiction example, searching for "Space Hulk" and "tiles" will turn up a bunch of results.