CoreWLAN will let you scan for beaconing APs (access points), but won't help you find unconnected STA (station) 802.11 interfaces. But this isn't a limitation of the APIs - it is the nature of 802.11. 802.11 STA interfaces don't "beacon" - only APs do.
As Tim said above, if the host / device your code is running on is a member of an 802.11 BSS (network), then you would use standard network discovery protocols above the 802.11 layer, such as Bonjour, which in Cocoa or CococaTouch is available via the NSNetService class and related classes.
What Tim said was not quite accurate though - Bonjour can find services on non-Apple systems (think printers, for instance). They just need to implement mDNS and DNS-SD properly.