4" spider

Looking for a 4" spider to mount my rocket launcher on. I already have the tube and base. Any leads or ideas
Tim
glassmasters@earthlink.net

What type of base? Murray brother, ect. Check out nautical outfitters they sell them, If not wait for murray brothers sale and purchase it from them. Cost is about $350

Thank's called Murry Bros, they said the easy way out was to change the whole thing to 2 7/8 ?? Did that months ago and it worked fine