If you go to a good sized pet shop they should stock tray liners in different sizes. You can buy stuff there to clean the tray with safely too. Basic rule is don't use disinfectants that make the water cloudy as they are toxic to cats. Well diluted bleach is fine [rinsed really well afterwards] or you can get sprays like clean&safe which kill bacteria and viruses that might lurk in the tray.
Scooping every day and a good cleaning once a week will keep nasty smells at bay and keep the tray nice for your kitty

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