there are quite a few standing stones in Perthshire with crosses carved on them. off the top of my head
<a href="http://www.themodernantiquarian.com/site/2295">Staredam</a>
<a href="http://www.themodernantiquarian.com/site/4088">St Adamnan's Cross</a>
I hear what you're saying about the crosses being carved in Pictish times, but I don't think that makes them Pictish. I've seen it suggested they were carved by priests from Ireland as they travelled to spread Christianity, rather than being carved by Christian Picts themselves
Cheers
Andy