It's all basically a trade-off between sensors size and image quality. Large sensor sizes give a better image but are harder to work with.

If you want an 8mm bead to fill the frame, then on a DSLR you need a 3X magnification (full-frame) or 2x magnification (APS-C) because the sensor eight are respectively 24mm and 16mm. This is even worse for the 4mm beads: 6x or 4x). Other cameras (compacts, "bridges") have a smaller sensor, so don't require as much magnification, but AFAIK their unchangeable lens alone won't let you shoot close enough to even reach 1x. So, two general solutions:

High-end camera (DSLR or mirrorless)

There are lenses for extreme macro (for instance this one) but they aren't cheap. There are other techniques (lens reversal) but getting them working right is a hobby by itself. In all cases, at such magnifications, your depth of field is very shallow, you will never get the whole bead in focus, your will have to take several photos of the bead, focusing on "slices" and then uses an application that selected the part with the best focus from the series of photos to produce an image where everything is in focus. This is called "focus stacking".

Compact/super zoom

You can use a ["close-up" lens)(https://en.wikipedia.org/wiki/Close-up_lens). Some are decent (Raynox), but are of course not the less expensive of the lot. This could let you get close enough for your purposes, with the caveat that the image will possibly be a bit soft. You still need a camera with some "expert" features like manual focus, manual exposure, remote control, and possibly external flash control. You may still have to do focus stacking.

In all cases, you'll also have to consider other paraphernalia such as a stand, a focusing rail, external lighting, and something to rotate the bead in front of a lens if you want to capture the whole surface.