Ellerby & Spudmore are the company name of the broom manufacturing team of Ellerby (given name unknown) and Able Spudmore, based in the Black Forest of Germany (QA9, Pm).
They launched the slow but sturdy Tinderblast broom in 1940. This was followed in 1952 by the release of the faster Swiftstick broom. Although well-made, neither broom was particularly popular as their designs had technical issues. (QA9, Pm).
Able’s son Randolph Spudmore was later to develop the Firebolt (1990s) (Pm).
Why a company with such English-sounding names (and English names for its brooms) is based in the Black Forest area of Southwest Germany is a mystery - possibly with an interesting backstory?
Lexicon list of Broom Manufacturers
From the Web
Writing by J K Rowling: Firebolt
Pottermore feature: Broomsticks
Harry Potter Wiki: Brooms
Tags: design manufacturers slow strong wizard technology wood