They've become as rare as hen's teeth, which by the looks of desperation in your post title I gather you're finding out
JLD Enterprises is OUT OUT OUT and I doubt they'll be getting any more back in. My understanding is all their new rifles are only coming with either the slim forearm (which sucks eggs) or one of their "tactical" forearms (which look decent, but nothin' beats the traditional wide one).
Florida Gun Works has some (the only place that seems to):
www.floridagunworks.com/Merchant2/merchant.mv?Screen=PROD&Store_Code=FG&Product_Code=1175&Category_Code=HKA+HK91G3+STOCKS - but the "factory" version is back-ordered. Don't know about the other which appears to be aftermarket, but price it the same so I would hope quality is on par. FYI:
don't even think you'll find cheaper prices...as rare as these suckers are getting, this will probably be the best price you'll find. I paid $110 for mine about 6 mos ago, and it is ABSOLUTELY worth it over the slim foream.
Good luck!!