Is it there any twitter client for Mac that can show in growl the result of a search? For instance, in real-time show in growl all results pertaining to the hash tag
Do they have to be Growl notifications?
Tweetdeck has to option to add a 'search'-column and let's you set the notification-options for that.
This results in a notification every time a new tweet matches your search parameters (and twitter's streaming feature makes it very fast)
You could have a look at Syrinx, a twitter client designed for Leopard (OS X 10.5+).
Here is what it says :
The application is free (donationware), although it does contain this warning :
Not having a Mac, I cannot test this application