Hi bulldog,
I used to have the same problem, living at home, your parents will see everything that comes in the post. I don’t think they mean to be nosey, but they are just interested in what you get up to. You could find a local sex shop, bigger ones tend to stock that sort of thing, but the chances are you will end up paying well over the odds and probably not get a very good one.
The other option is that to tell them that you are ordering an anniversary/birthday present for them, so if a package arrives they mustn’t open it. Then get them an equivalently sized pressy.
That still leaves the danger of discovery. I don’t know what your parents are like, but mine (well my mum) had a nasty habit of deciding to randomly tidy my room and no matter how well you hide stuff they’ll find it. I once came home to find my porn collection (that I thought could never be found) laid neatly out on my bed. I didn’t speak to my mum for a week.
Hope this helps.
LB