I have used Farnell to get this type of plug and socket before.
They also sell the type of plugs wich can fit both this type of socket and cigar lighter style sockets, with the addition of a (supplied) adaptor ring.
Although, if you want to have stuff plugged in whilst riding, I would recommend using the smaller type of plug since I find my knee can knock out the longer plugs!
Click here to see them.
Sockets
You might be able to get them more cheaply from other sources (and I think Farnell have a minimum order value too), but I have always found them most reliable.
HTH.
Oh, I almost forgot to mention, if you do use the
smaller plugs, you'll need to be handy with a soldering iron because there are no screw-terminals in them!
[ This message was edited by: tcowjww on 2006-01-11 11:11 ]