Just a quickie in reply, remember that grit is for the chooks to help them "digest" their food in their gizzard, it has no bearing on the eggs (well except if their not getting enough food/nutrients etc). So if your chooks are really free ranging (as in all over the place...within reason I suppose although mine have 2+ acres to wander aboot) then they should be able to pick up enough grit to help with the mastication process.
You are probably thinking of calcium (oyster shell) which they do need to help form good, solid, hard egg shells. So easy solution is to get hold of a bag of crushed oyster shells and leave a wee tub (like the smallest plastic salad to go type size from yer local tesco's etc) for them to peek at.
POL's will occasionally produce soft shell eggs which is not a problem as they are just getting the hang of the whole egg thang so will occasionally produce a "duffer" for a few weeks but it will stop. If it doesn't, then (a) not enough calcium or (b) off to a vet me thinks.
Oh and the reused egg shells helps with the calcium but you should really get some crushed oyster shell and NO it doesn't help with the grit thang.
Most on-line retailers sell oyster shell which IMO is all you need. Free range chooks will find enough grit for themselves (mine are partial to a wee peek at the fallen bits from our harled walls en route to their various fields!).
Crips, that wasn't quick! Anyhoo oyster shell not grit methinks & give them time to mature