All the info you're looking for is there in either link or text form. But Basically, The Istapp is one of 3 ships in the Dereri Sector that you have to destroy to get an accolade. Finding the ships first is by rare chance.
Indeed... The most common of the 3 ships seems to be the Desna. I have regular encounters with this ship around outpost 3.
If you want a "look" at it, that is probably the best place to start.