Crunchier breadcrumbs

You can make very crunchy crumbs using a dehydrator (probably also a very low < 200 degree F oven). I frequently crumble leftover cornbread, then dehydrate, to produce super crunchy cornbread crumbs. I am sure it would work with any bread. Using this technique with cake also works nicely to produce a crunchy topping for sweet applications. BTW 200C (the temp the OP provided) is way too hot. You will brown (then burn) the crumbs rather than dehydrate. Use Less than 200 F or in Celcius, less than 93C

try leaving them in the oven for longer and/or at a higher temp. exactly how long and how hot really depends on the type and freshness of the bread you are using. but it's certainly easy enough to tell when they are ready- if you pull them out and they are still soft, put them back in for a few more minutes!

My go-to for many years (before I knew about panko) was to use cracker or cereal crumbs. The shape of the crumbs end up being less round, which allows you to get a texture similar to panko.

As they're already crisp, they also work fantastic in baked applications. But you may need to adjust your seasonings based on the crumbs -- crackers already have salt in them, and it's best to stick to an unsweetened cereal like cornflakes or rice chex. Cheezit crumbs make a fanstastic coating for baked chicken tenders.

If you're really set on making panko, however, I suspect that I discovered the secret in a video that dbmag9 posted in a comment in Is panko just pretentious breadcrumbs? -- use a coarse grater. I haven't tested it, and you may need to find the correct moisture level (or freeze it?) to pull it off, but they say "the bread is ground using a proprietary screen" around 3:20 in, and the images look like the "screen" is a huge grater.

The important part here is the size -- if you're not getting large chunks of bread as you grate it (which is going to be trial & error with the staleness of the bread, and might not be easy on a standard grater), you're probably better off just using the food processor and just pulsing it a couple of times, then sifting it so you only have crumbs of the right size. (pass larger bits back though; save the smaller crumbs (aka 'fines') for meatloaf or similar where you're not looking for texture).

(I don't think I saw the Alton Brown video that Jolenealaska had linked to in the comments above, which is now dead ... it's possible that had more specifics ... although a vaguely remember something about panko being made in sheets, not loaves, so maybe that was it, with a different technique).