Hey Keegan! Congrats on your new purchase! It's a beauty!
I'm a lefty too and I'm in the process of getting someone make a lefty pickguard for my Jaguar as well. I've got a local fellow here who's gonna make a black 3-ply pickguard for roughly US$25. Ishibashi does sell replacement pickguards too...but they're pretty expensive cos they have Fender Japan to custom make the lefty pickguards. A tort one costs up to 10000 Yen, which is around US$82. Personally, I'd take my existing pickguard to a local shop to have it traced so that it'll fit exactly. I've heard horror stories from this forum that even some CIJ/MIJ ones don't fit their Japanese jag to a T.
I'm sure there are a few other online stores that sell MIJ pickguards but lefty ones are few. One of them is http://www.terrapinguitars.com, which can set you up from US$40+ to US$70 for a tort jag pickguard (not sure if they conform to CIJ/MIJ template tho).
I've dugged out this thread on where to get pickguards and I think it'll point you in the right direction: