Knight Manufacturing had developed a special rifle that used standard AK47 magazines, but retained the AR15/M16 ergonomics.
From what I understand, they had to change the lower and upper dimensions to accomplish this and the rifles were developed based on a specific request from the Dept of Defense for use in very specific circumstances. I heard the price of complete rifles was around $4,000 and they have no plans to release them to the civilian market.
If you want to stay with 7.62x39, best bet is to try the various AR15 7.62x39 magazines (some work, some dont and some can be made to work with a little massaging with a pair of pliers).
Another option is to wait for the 6.5 Grendel available for order in February 2004. It is an improved version of the 6.5 PPC which is a relative of the 7.62x39, but offering vastly improved ballistics. Alexander Arms will have magazines for the 6.5 Grendel and .223 magazines can be modified to function as well.
Even if the Knight was available, it would not be able to be sold or owned in California. I think the only new AR lower that can be sold in California is the DPMS single shot model.
If you aleady have a AR lower that predates the restrictions and you did all the registrations, then you can buy either a 7.62x39 or 6.5 Grendel upper and enjoy.