For to get the manufacturers listing with BrandBox Module.
This module is able to list all manufacturers in different way of display.
Display by Dropdown, by List or by Alphabet sort-order.

By simple and sample css rules is possible customise it, like alphabet buttons, height of dropdown, height of list and height of alphabet, with or without scroller.

Also, BrandBox is able to refine the brands by categories, by admin settings;
You can see only the manufacturers that have products present in selected category.

Demo: spazioeffe.ovh/opencart