Hey Sue, hmmmmmm.... making me think huh
Well, according to wise Jeremy and the RAE ("Real Academia Espa�ola", de la lengua), neither the word "Mejorero" nor "Mejorador" exist in the Spoanish language, sorry
Just go to
http://buscon.rae.es/drae/drae.htm to do the search for yourself if you like.
I loved that comment about "Matadores" undoing bulls

Jejejeje.
Normally we add the "ador" or "ero" in the masculine at least to the verb and/ or noun to describe someone who carries out that verb or a place where it is done.
There do not seem to be any rhyme or reason nor rule of thumb to this and it works with either one ending or both, depending on the word used:
* "matar" = "to kill"
hence...
"matador" = "killer"
"matadero" = slaughter house"
* "cazar" = "to hunt"
hence...
"cazador" = "hunter"
"cazadero" = "hunting grounds"
* "comer" = "to eat"
hence...
"comedor" = "dining room" or "someone who eats a lot"
"comedero" = "someone who eats a lot". (also means "trough", oink oink!).
You also have some "frases" made from some of these words such as "limpiarle a algui�n el comedero" which means to fire or take soemones job away (basically leaving him or her without the measn to earn money and hence eat).
* "bot�n" = "button" (any kind)
hence...
" botonero(/a)" = "button maker" or "seller or buttons"
but the word "botonador" on the other hand does not exist in Spanish.
* "lata" = "tin"
hence...
"latonero(/a)" = "tin worker" or "tine salesman"
but the word "latonador" on the other hand does not exist either.
***Jer's Useless Historical Note of the Day for those who Care: many of the streets that surround the Plaza Mayor of Madrid are named after those professions, for example the "calle de latoneros", "calle de botoneros" or "calle de bordadores" ("bordar" is a verb which means to "embroider" hence "bordador" = "embroiderer")
Anyway Sue, just the fact that you have been asked to help name a motorcycle gang scares the he&% out of me
It may be basic but how about "los majos"? kind of like it myself.
Saludos,
jer...
p.d. and no, don't even try "los majaderos" for it means "amateurs" and "stubborn" or "hard headed" (figuratively).