Well, it would be an awfully short game if you could just use persuade to get the location. The Jedi council wouldn't even need you- any one of the Masters could do it! On Manaan there is some talk about how the Sith shield their informants from interrogation- perhaps they have done the same about the Star Forge location? Or perhaps they perform some kind of memory wipe on most of the ordinary soldiers who have had cause to know where the Star Forge is?
It did occur to me, however, that you might not need the 5th Star Map. On the Leviathan, the bridge computer says that a course is locked in for the Star Forge, so since you are in the computer anyway, you could note down the coordinates. Although I suppose hanging around an enemy ship any longer than you needed to isn't a terribly good idea...
That there are Republic ships there doesn't surprise me. Carth is Republic military "on loan" to the Jedi, so I expect that once you got the coordinates from the last Star Map he'd contact headquarters with them. If they were faster, or closer, they might well get there first and be just sitting there waiting for you to show up and take care of Malak. I agree XRichX, they would be fun to explore.
Now, the part I'm really finding odd is why HK happens to speak the Sand People language. If I was designing an assassin droid, fluency in obscure languages would definitely be a must!

Best I could come up with is that he was a modified protocol droid, and his language ability was just left in (no memory limitations in the future, I guess).
Partial spoiler
It didn't seem like Revan had spoken with the Sand People before, in order to get the map the first time. The Sand People don't recognize you nor do they or the Jawas make any mention of other outsiders who have been by looking for maps.: