Hi Marc,
Here's the FFT tube prices
http://www.freedomfightertactical.com/order.php
Here's Kip's Carriercomp tube (that's what I use)
http://www.shop.carriercomp.com/category.sc?categoryId=4
You can do it yourself. It's not very hard. Kip's instructions are in post number 2 of this thread:
http://www.benelliusa.com/forum/showthread.php?t=17726
Later,
Hookster