No, there's nothing off-the shelf. I remember this being asked before and I believer the answer was that there's pretty much no room for a longer stroke because the cams sits too low. Theoretically, you could off-set grind the stock crank since that wouldn't actually raise the rod journal, so you wouldn't have any less cam-to-rod clearance. Unfortunately, off-set grinding is also a bit tricky, since the 350 (and 300 and 340 too I believe) has 2.00" rod journals, which are just about the smallest you can get in typical muscle-car engines. Apparently small journal SBC guys (who also have 2.00" journals) are starting to run honda bearings (about 1.875" I think), so that would be a possibility, although you would probably have a limited and costly selection of rods to use, in addition to needgin custom pistons. So, it is technically possible, but not worth it, since even if you did increase the stroke the full .125", you would only go from 355 ci to 366 ci (bored +.030). That is unless you were planning an all-out build that would require high-dollar custom parts anyways.
