Zinger is no longer in business. I can't verify this but I heard family members did not want to continue after the death of the founder of the company.
You might try the MECOA website. At one time, they still had a bunch of Zingers but it has been a long time since I looked at that to see what was available.
You are right about the Zingers being a pretty good prop kit. In stock form, they are terrible. But, when reworked, they can be made to perform quite well, if you know what you are doing. The issue here is time. Is it worth the effort? I say it is if this is the only way to get what you want.