Just a couple of thoughts. Dont hold anything i say as gospel but A gas block might not be the best accessory rail. If anything on there gets hit or catches on anything it could move or dislodge the gas block, depending how secure it is. If you go with a clamp on I wouldn't advise attaching any accessories to it. Second, the gas block gets f'in hot. Make sure any accessories you use can be attached to a gas block (no plastic flip ups like the magpul BUIS, to the best of my knowledge)
If you can't find what you are looking for then there may be other options that would allow the use of a standard handguard, or a magpul handguard which has options for attachments.
If your concern is getting the front sight tower out of the view without going to a low profile with a rail, there are fsb gas blocks that have integrated flip up sights. They aren't cheap tho.
If you used something like that in conjunction with a magpul handguard with light attachment you might get what you want.
Wolverine supplies has gas blocks like that