I got one from WD Music - [url="http://www.wdmusic.co.uk/category/Pickguards/Fender_Basses"]http://www.wdmusic.co.uk/category/Pickguards/Fender_Basses[/url]
Have a look at the Jazz Bass Mexican section, they've got a good selection.
[attachment=6909:MIMScratchplate1.JPG]
[attachment=6910:MIMScratchplate2.JPG]
The photos above are of my MIM Jazz with its WD Music scratchplate.
As David Nimrod said; the fit isn't perfect.
I had to trim the scratchplate around the pickup, I've got Wizard 84's pickups.
The recesses for the pickup cover mount screw holders were too small on the neck side (I hope that makes sense).
It was very quick and easy to enlarge them with some small files.
Also, as you can see in the closeup, it doesn't match up with the control plate.
It's about 2m narrower on each side, which I can live with.