I've got a pure energy 48in 3000 psi tank, simply because that's all i could afford, and it has no problem keeping up with the x-valve, the only time that you'll find problems is if you're trying to shoot in excess of about 26 bps, which you won't ever have to worry about.
As for the sear, i honestly have no clue, never heard of that happening. A sear can be had from
www.airgun.com, and depending on whether your sear rod screws out (rt sear) or if it just has a fairly large steel peg that it rotates on (the minimag/automag sear) it can be cheap or somewhat pricey, the RT sear is pricier.