One of the biggest changes I've noticed since getting back into the hobby is where you buy models in the Sci-fi and Real Space categories. New releases seem pretty much limited to Star Trek, Star Wars, and the Space Shuttle. Anything outside of these are simply reissues of older kits. I'm hopeful that new companies like Mobeius are successful and that others will follow.
Retail stores- Except for Hobby Lobby you can pretty much forget these places that were once my ONLY source of models.
Local hobby shops- Even back in the old days there was only one of these and it had a poor selection. It still exists but they mainly do RC and trains.
Online- Kinda hard to believe but even these guys are pretty limited on their stock. One exception, if you are into the space shuttle. I lost count of how many different versions are out there. Seems like every model company puts out at least two or three.
"Garage kits" (resin)- These guys do a great job and provide the hobby a great service, especially to niche markets. However, since they have such small production runs I cannot afford to buy very many of them.
Ebay- This has been my major source since I returned to the hobby. Its a little tough sometimes paying $30-$60 (not counting S&H) for a kit that only a few years ago I remember seeing for $10-$20. Fortunately I'm a builder not a collector cause it would be a lot worse. I don't care that the model is a Glencoe Space Station and not a Strombecker Space Station.