I assume you're looking for a folding stock similar to those offered for R-870s and M-500s. Sorry, it can't be done. Unlike the R-870, the R-1100 and R-11-87 both have an action spring housing (shown in red) that extends behind the receiver and well into the butt stock.
The M-930 and M-935 have an in-stock return spring housing similar to the Remington design. Legal issues aside, there are folding stocks available for the Saiga-12.