Go to where they sell projectors, commercial entertainment equipment and such. or kata the normal VGA into two and do your own extension with wires, some solder and a tape if you cant get a new long one.
Go to sight and sound computers. You will get Vga cables of whatever length.
If you insist on joining the cable get cable connectors. Lakini kama lazima soldering, take the cable to popman house third fl. 1st shop on your right as you exit the stairs ask for someone who can do that.