I was able to find a source for these:
Find many great new & used options and get the best deals for M6 M8 M10 Round Head Phillips Screws Flat/Spring Washer SEM 304 A2 Stainless at the best online prices at eBay! Free shipping for many products!
www.ebay.com
They have the flat washer along with the split lock washer, so not exactly like the OEM screw, but the flat washer could be removed. From China/Hong Kong/Taiwan, but probably OK - they're just screws, right?
$6.89 for a package of ten (M8x20mm), plus $2.35 shipping. I'm assuming the thread pitch is 1.25, but don't know for sure.