Currently about all of "8-bit micro" games that I know is either abandonware (which is a gray area) or free fan works. But is there some kind of shop, market, some place where you can purchase these games, or other software fully legally for money? Some kind of retro-shop, or such?
There are quite a few... On the homebrew front for example, the AtariAge store sells packaged homebrew games for 8-bit Ataris (and now Intellivision), as does pro(c) (along with its magazine). You can also find stores which still have "old new" stock of games, computers and accessories; for example Best Electronics for Atari computers and consoles. There are no doubt others for other platforms!
For the ZX Spectrum and MSX there is Matranet, which sells physical versions (e.g. tapes and cartridges) of recent releases. http://www.matranet.net/boutique/boutique.php