Replacement compound bowstring and cables

I bought a 2nd hand compound bow in LH recently. A Perfect Line, currently set up for 50lb, 28" draw. 30" draw would suit me better, though. I have 3 questions:
1. The string looks a bit rough so I thought I'd replace the string.
Any idea where to buy these?
2. I only have the string length written on the bow (58") but not the cables. The bow is pretty obscure so no info online. How do I find the cable length?

3. Also, does anyone know someone who could adjust the draw length in the Wairarapa?

Any thoughts (other than I should have done my homework first)?

Identify your target beyond all doubt because you never miss (right?) and I'll be missed.

Advanced archery in Auckland do strings. Adjusting draw length depends on the bow, some can be done real easy, others need new components bought and added with the help of a bow press.

Yep. Depending on cam design, you could require new modules, or in some cases a whole new cam.
Most of the cheap Chinese bows are very adjustable though. If you replace the string, replace the cables at the same time.