I think that Sparkfun should carry mono jacks and connectors. They don’t have to make them just order and stock them from a supplier.
They are pretty much audio cable connectors and jacks. It is really simple to install the jack into a project enclosure you just drill a hole and tighten a nut. The connector has solder terminals they you attach wires to and then a sleeve that goes over it to cover it up.
I use these all the time in project enclosures (for power, sensor connections, and any external connections).
This is what I am talking about.
This is the jack that is put into the enclosure (again very easy to install).
http://www.radioshack.com/product/index … Id=2103453
This is the connector.
http://www.radioshack.com/product/index … Id=2062452
I think that Sparkfun should stock both the connector and the jacks in 1/8in size (and 1/4in if possible) as well as have the connectors available with red, black, and if possible other color sleeves.