Ordered 25 cement plugs for $5(free shipping) from mrs.salty and got them in 3 days. If you are looking for plugs quick. I would rinse and dry them though.
or make your own.. well thats what i am doing. depending on what cement was used i would be careful of it leaching. I know when you make plugs or rock you have to cure them for a few weeks to a few monthe depending on size.
They were listed as cured. I don't have time to make my own. I guess I will find out, but they are small and they came in wet, so I am guessing they were in water prior to shipping.