From light blonde to dark blonde...please help

I'd recommend test strands. Lightened hair can be really unpredictable and pick up the base colors in everything. This means if you cannot buy at a beauty supply shop, it will be even more unpredictable because you will likely be getting boxed dye which does not give you the base color information to work with. Since your hair is so lightened, it is very porous, so whatever you put on it will likely come out quite easily (even permanent probably wouldn't stick more than a couple of months), but, anything will add more damage over bleached hair, so testing is good, not only for the color but to make sure you don't hit the breaking point.

So, I would buy a dark blonde, then test it. You can just mix up a small amount of it to use only that and save the rest. If you wait a few weeks after doing it, you can also see how your test strand does after a few washes, (whether the dye just comes out or goes a funky color because its on lightened hair). (I just did this on my lightened hair which was then dyed brown, I got dark brown semi-permanent and it came out purple black! Unfortunately the test strand is only getting more purple each time I wash it, so I'm probably not going to be using the stuff).