Catgrass is Avena sativa, AKA Oats. You can WS it, although it doesn't need stratification, or you can grow it indoors easily. There are a million kits available on the web. Just be sure you don't let the cat eat it after it develops awns (goes to seed). It's only safe when it's immature.

My cats never ate grass or nibbled on houseplants, but I fed them on a BARF (bones and raw food) diet, and they had no digestive problems.

I grow wheat grass for my cats all winter in a bowl at least 3" deep. It lasts about a week, so I usually always have some seed in a jar sprouting. The photo shows a change out from a previous year.
You can always make a small 'dome' or 'cage' out of chicken wire and keep the container covered with it until the grass is high enough to give to your cats. I set the bowl of grass near the window for them when it is at least 3" tall. Until it's that high, I just keep it near a table lamp.
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What a great idea. I even have indoor lights I could start them under. My cat had more issues when she was younger, but I always give her the hairball food. We've recently started supplementing her with canned food--more for us because we enjoy watching her gobble it so happily--but I wonder if she gets enough of the digestive benefit from the dry food, now. Haven't noticed any messes, though the dogs are so helpful with clean-up.LOL. I believe I'm off topic.
I would think the grass would do fine with winter sowing, but it won't sprout until warmer weather, so that doesn't help the cat right now.

Martha

I have grown catgrass indoors in the winter just near a window... super fast growers, but it was for guinea pigs not cats! I also grew italian parsley and dandelions for them. I actually ordered large leaved gourmet dandelion seeds from Johnny's seeds for them! My piggies were quite the foodies and a lot of fun.

Thank you all for your responses!!! They really helped. Trying to grow some catgrass indoors now. Planted them in kitty litter containers that are clear and removed the lid adding holes for ventilation and drainage. Taped up the sides to keep kitties out of them. If that doesn't work, I may have to try the bowl and jar idea! Thank you for the picture! It helped a lot!!! Thanks so much to all of you!!! :)

Thank you all again for your help! The catgrass did fine in the plastic containers. I cut off the top of the containers completely when the grass was tall enough not to get mutilated by my furbabies! :) I Put dirt in a pot to start catgrass in the following morning, and one of the kitties dug out the whole pot of dirt. Little stinkers! LOL! But they are enjoying the kitty grass in the plastic containers. Bought some more dirt, so I could start more. Thank you again!