Joe Swanson make them, they are expensive but they feed smooth and are nice and loud with a good flash. Do a google search for him, his site will come up. He also makes the only 7.7 blanks that will feed reliably. Type-99s are notoriously finicky when it comes to feeding short blanks.
Another company is Atlantic Wall, search for them as well. I have never fired theirs, but they are cheaper than Swanson. Problem is that their supply is eratic.
I have about 25 or 30 of Swanson's on hand, he does a fine job making them.