You could try www.nippon-motors.com, or try calling Foreign Engines, Inc. in Lynnwood, WA, or Sunrise. Those would be my two first tries (besides eBay).
or will the stock tranny in the 99 civic ex able to place a lsd in it.
Oh, I was under the impression you were looking for a b series trans, since they're generally the only trans that come with LSD. You could try to land a JDM D15 LSD tranny, though I don't know if it will mount up to a D16Y8. Your only other two choices that I know of would be OBX and Quaife LSDs. (I don't consider Phantom Grip a choice.)
Just go with a OBX. They are pretty good for the money I have heard no complaints from a couple friends that have it... I got a Quaife in my car and its doing the trick nicely but its a lil more pricey.
to be totally honest... lsd wont help that much at the track unless your putting down mad power. I have a friend who ran 11.84 with a open diff. LSD is better for around the town driving but not that benificial for the track. Your money would be better spent elsewhere IMO.