chick grit- oyster shells??

Grit and calcium/oyster are different things. You do not need the calcium/oyster until they start laying. The grit is for grinding up food in the gizzard. A lot of people suggest the sand, or sometimes they get chick grit at a pet store. Some caged bird grit is fortified with calcium.
It's OK to worry, it keeps you sharp. I'll admit that I didn't know about chick grit when I had chicks years ago. Never used it and the chicks were fine.

Imp

You may be able to find parakeet grit at a pet store.  I forgot Imp's warning on calcium fortified grit though.  Good point.  You can use course sand, maybe construction sand.  The play sand is too fine and smooth.  They will use it as grit, but it will basically just pass straight through their system.  I'd rather they used that volume for food with nutritional value.  Grown chickens use gravel pieces anywhere from the size of a pea on down as grit, but chicks need something smaller.  For adult chickens I often suggest just gathering small gravel and sand off a gravel road or driveway, but only if it is not salted during the winter for ice.  They cannot handle that extra salt.  I do not recommend this for young chicks since much of the gravel is crushed limestone and they can get a lot of calcium from that gravel.

Oyster shell should not be given to chickens until they are of laying age.  It is too soft to be used as grit.  You need something harder.  But the stronger reason to not use oyster shell is that the extra calcium it provides can hurt their internal organs, I believe the kidneys.  They do need some calcium to grow properly, but that is provided by their starter.  In general, too much of anything can hurt them, but excess calcium is something that definitely can hurt them.  It is not that they will immediately fall over and die the instant they eat a piece of oyster shell (one piece will not really harm them anyway) but consistent excess calcium can cause long term damage which weakens them and can eventually kill them.

I have actually seen "chick grit" and "poultry grit" as well as oyster shells.

I think the chick grit is just a much smaller grain than poultry grit and is meant as a free-choice supplement for range-chicks.

I have a bowl of chick grit in the coop with my 2 month olds, prolly when they start laying eggs and getting oyster shell, I'll switch it to pultry grit.

just go to a local building suply store- lowes, home depot, or what ever is near you and get a bag of all pourpose sand it has every thing from small coarse pieces to larger pea sized pieces so the chicks can pic up what ever suits them as the grow and get biger , it comes in 50lb. bags and they love to play it also. i found that this worked best after trying the parakeet stuff (wich gets expensive because they go thru tons of it) and play sand wich is too fine , they just pass it through.

Yes, what mistyfeather said. 

I, too, use construction "all purpose" sand purchased from Lowe's in 50# bags.  I also put some of that sand in plastic kitty litter pans, and tuck those in covered areas of the run so the chickens can still take their 'dust baths' in the sand and pick through it when it's rainy.   There's a spot in the run where I toss the rest of the bag o' sand for them to use in the same manner (when it's not rainy).  Every few months, I buy another bag and replenish the pans and the sandy spot.  (I save some of it for grit, "in case" I get any chicks, so I can provide it when I give them treats.)

I don't mean to hijack this post but I have another question along these lines. We bought a pound of #1 chick grit at the feed store and for some inexplicable reason, mixed parakeet grit with calcium in with it (small box). Will that diluted amount of calcium hurt my girls? Should I throw it out and just get another pound of just grit?

they will be fine the first box of parakeet grit i got had calcium in it , they used the whole box and were fine. i think it is in too small a dose to hurt them , i just wouldent purchase any more

I was able to find washed playground sand at Home Depot; 50lb bags for about $3. Nice sand - not too dusty and I figured if washed for kids was probably fairly safe for the birds as well.