I was able to find a really great deal on a pickguard on eBay by seller choppersmusicllc. They've got a few other lefty items up for sale, and my guess is that they offer more than what they put online.
The pickguard I got was a tortoise shell, and I swapped it out for a white one that came with a burst MIM J that I purchased a few months ago. It didn't fit on right away, but the modification I had to make was so quick and insignificant that it was definitely worth the $6.89 total that I paid for it. I only had to sand a tiny bit of the area where the pickguard butts up against the control plate — in that little "V" area. It took all of 10 minutes using 400 grit sandpaper. I am pretty confident stating that this pickguard fits on this bass better than the pickguard on the other J I have.
The results are below:
Attachment:
Burst J with Tort Pickguard.gif [ 499.1 KiB | Viewed 6483 times ]
I purchased a couple pickguards from Guitar Fetish a while back and they did not even come close to fitting, so they were returned. This was a much better option, in my experience. Your mileage may vary.