Unfortunately, you cannot use any of the cylinders that they sell, as far as I know.
You need to read this manual
http://www.usfirst.org/uploadedFiles...ics_Manual.pdf
and go to the Bimba FIRST page
http://www.bimba.com/FirstFree.aspx
and order your 3 free cylinders there, and if you need more cylinders they need to be exactly what is listed on that page.
Also if you only have 8 to 10 inches for it in the retracted position, you won't get much travel at all, especially with the large bore cylinders that can actually push with a lot of force.