Perazzi made two choke tubes that had a short knurled section at the top of them (muzzle end) that might fit your gun. One had threads toward the top, the other had threads toward the bottom. Figure out which of those you have. Once you've done that, you could either search through ebay.com and gunbroker.com, where they sometimes turn up.
Or if you want new ones (and excellent ones at that), I'd look at: teaguechokes.com . You'll need either the Perazzi "MT6" or "MX4" depending on which end of the choke tube is threaded. You can see their website for pics showing what I mean.
If you have the "MT6" style (threads toward top) and are okay with used ones, I might have some spare Perazzi original ones I can sell you for relatively cheap. Just PM me which constrictions you want and I'll check and see if I have spares.