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I don't know if you are still looking about información on this plate or you allready found something since you post it half a year ago.
I have been looking on the internet lately and there are some similar plates for sale on different sites. All of them unmarked, handpainted, handmade, with pierced rim and with traditional Imari-style colours and motifs.
There is a general consesnsus that these are authentic Imari (Arita) japanese antique porcelain from the end of the nineteenth century.
There you have an example: https://www.onekingslane.com/product/50057/3378790
I hope I could help you.
Cheers and happy 2016