I have to agree with the others on PGOs. I've got no use for them. That said, I do actually hunt with a pistol grip stock. It's not on a Maverick, but that's beside the point.
It looks like Choate makes a telescoping M4-style stock for the Maverick 88: http://www.riflestock.com/store/do/product/02-01-27
I'm a lawyer, but I'm not your lawyer. If you need some honest-to-goodness legal advice, go buy some.