Guys I have a question on cable steering.

I plan to re-rig my cable steering on the STV because I added a 6" jack plate and the cables aren't long enough with the additional offset.

Where can I buy new steel steering cable?
My current come without the plastic sleeve but I remember years back on my other boat, the steering cable has a plastic sleeve thus minimizing cable wear on the pulleys. Does it matter if I use plastic sleeve cable to steer a 260 outboard? Comment suggestions and advice welcomed