Where can u purchase a fuse for the alternator.....the auto parts stores around here say there is no such thing but there is a fuse blown on mine

 

Some car have a fusable link. it's basically a fuse embeded in the wire. Your best bet is to run a new 4awg wire and use the same fuse/holder you can use to power an amplifier.

Make sure you use a fuse that have an higher rating than what the alternator can put out but do not exceed the max recommend rating for 4awg at the lenght you need.

Also for the wire make sure you use true copper (OFC), most place will try to sell you CCA (~90% alu/10% copper) and 4 awg CCA will be limit for the factory 100A alternator