The cable, or any soldering you can do internally, is only useful if you are going to be doing some of your own development, rather than a one-off programming of one machine (there are lots of people, myself included, who will gladly program your machine for you).
In the USA, sparkfun.com has 3.3V logic level FTDI USB-to-serial cables (Vcc is 5V, though, so you can't use it for powering the calculator). They also stock pogo pins (that's what the spring-loaded contacts are called). The contacts on the programming cable are at 2mm pitch, so you'll have to get either a perfboard (or, better yet, a 2mm pitch IC socket), or make a little jig yourself to align the pins, and then solder the cables from the FTDI cable, along with your own reset and erase switch.
Programming is very quick, so you can actually hold the cable in place by hand, you don't really need the side clips. You just have to be careful to plug it in the right way!
Mill-Max makes a large selection of pogo pins and connectors, unfortunately, the preassembled ones are only on .1'' (2.54mm) centers, so they can't be used as-is.
