Extending the cabling of my left channel

My 2 channel system currently plays across the width of my living room and I want it to play the length of the room to improve the sound. This will require me to move the right speaker to the left side of the room. The wire will not be long enough so I will need more wire. My speakers are "TRI" wired so we are not talking a few extra feet. I would prefer to find the same exact wire for the extension but unfortunately it is the Mark Levinson HF-25c which is hard to find. Does anyone know where I can find this wire? Also what is the best way to attach the wire to what I currently have (solder it or butt splice)? Finally if I am unable to find this wire what wire would best "match up" with what I now have and would there be an audible difference?