I did a search for Pino the twitter client and it comes up but when I click more info it says here is a screen shot of it here:
It looks like Pino hasn't been updated in almost two years (since January 2011). It was only officially available in Ubuntu 11.10 Oneiric., and is not included in 12.04. That's why you get the "not found" error.
You can install it from this PPA:
Now open Software Center, and search for Pino. You should now see an Install button. Install Pino; I tried it on 12.04 and it appears to work.