Ata shotgun stock

I have an ATA semi auto shotgun that had the stock shortened (maybe an inch tops), before I bought it for my son to use a few years back. The model with a separate piston sleeve for heavy and light loads
I've ended up using it lately and I've lengthend it back for me and him, but not really happy with the result.
Plus my method makes it a pain to tighten the stock bolt if it comes loose.
Does anyone know of a replacement rear synthetic stock and possibly the shims floating about?
Being from Turkey does it share the same mounting pattern as others?