Is there a way to add another sleeve without using a tool? Can I use spectra as a sleeve too?
I'm going back nearly 20 years!
The sleeves I used were significantly larger in diameter that the outer sleeve of the spectra, so there was no issue with threading the line through.
Your local kite shop may be a good place to start as they should have the line and sleeves. Power kites and the kitesurfing kites will all have substantial breaking strain lines!