try gemm.com, or amazon. Amazon tends to have the OOP CDs, used, through their affiliated sellers. At least I think they do.
Gemm, be very careful because a lot of sellers simply list everything, and their ability to get "special orders" is even less than Tower, and the difference is, they may charge your credit card in the meantime. Not worth the hassle, so check the seller's feedback and also whether they have things in stock in the first place.
If you're interested in Japanese pressings (I'm not sure what's in print at the moment) try Mr. Tanno at early records. http://www.earlyrecords.com
You can get his e-mail from the site, and if its in print in Japan, he can locate it.