Best way to fill my bsa r-10 mk2 3,300psi

CF tank. As big as you can afford and new as you can afford. Depending on how close you are to a fill station will also limit your choice. I have a steel 3500 tank that's a hog compared to my Scott tank. If I started from scratch I would bite on a scba before the steel tank. Only benefit of my steel is the lifetime is never ending as long as it passes the hydro.