Hi Ted,
I have not heard of offsets or lines being available anywhere for any Carleton canoes... (though it is certainly possible someone has taken them off somewhere along the line). Since Old Town still owns the Carleton brand, they may not be thrilled if someone started selling lines...
The Indian Princess is simply a fancy model of their regular canoe (sort of like an Old Town AA grade). You may be able to find someone who owns a Carleton that will let you take lines off. I would think the older the canoe the better the shape, and if you want a pre-Old Town Carleton, look for something built before 1910.
Good luck!
Dan