There's very little after market support for smaller brand, Turkish made shotguns, also companies like emperor arms, and hatsan really don't care about their customers after the sale is complete.
I always I highly encourage people not to buy from these companies if modding and having aftermarket available parts is important.
Id say bring it into a gunshop with the sight removed and look at different brands to see if there is something you could modify to fit.
Or see if gunsmith can make something custom.
Outside of that your stuck with what you got