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there are several good ones including the wilson/scattergun tech, the sage etc...
check out some of the dealers here ie TSE they may have them
the bad news with ordering form Brownells is being a shotgun part & porbably over $100, you iwll need to get an export permit which delays stuff
If you're looking for something a little cheaper than you could try the Williams WGRS rear sight. It has a larger ghost ring aperture available for it as well. I've been thinking about putting it on my Norinco 14".