What you want is BeeSoft's ProTA Gold, similar in functionality to MetaStock and Tradestation. I sent them an email, they said the OS X version is entering beta testing this month and should probably be released commercially first quarter 2003.
http://www.beesoft.net/
It seems to be a small company, so they're open to suggestions, bug fixes, and improvements - unlike the lack of response I always got dealing with the Tradestation guys.
I found BeeSoft through this link on MacCentral, which details quite a few different apps, some of which are dead links, sadly...
http://maccentral.macworld.com/news/9904/23.migrationkit.shtml
Also, there's always the online java-based apps, like ProphetCharts, which is good, and mostly free, if I remember correctly.
At worst, use VirtualPC or SoftWindows to run Windows apps on your Mac until the companies port their software over. If you NEED Metastock or the like, write Equis! They don't know you want a Mac version unless you tell them!