Hiragino Sans GB W3.otf and Hiragino Sans GB W6.otf are installed both by Snow Leopard and Lion in the main /Library/Fonts/ folder. Are they actually missing from that folder, or are they just not showing up in your applications?
Since you don't have the OS disks, you can still extract them from the Lion installer. If necessary, login to your App Store account and download the Lion installer again. When the message to begin the install comes up, you can cancel out of it like any other program by pressing Command+Q. That will leave the installer in the Applications folder.
You can of course also just let it install, but the installer will be deleted at the end. I suggest quitting first so you can make a backup copy of it. Then you have it on hand if you need to do a reinstall rather than waiting for that very long download to complete again.
Once in hand, you can extract the two fonts you need from the Lion installer. Follow the directions at the bottom of Font Management in OS X.
I may receive some form of compensation, financial or otherwise, from my recommendation or link.