Over the many years in my career field, I have always found it difficult to find useful information...
Below are some websites I would recommend for personal use:
This is a forum based website that has used/new instruments for sale, auditions both professional and school based, and other useful information for tuba/lowbrass
A job database regularly updated for an avaliable job for any instrument, tuba included!
The "tuba/euphonium" website that every student MUST be a member of. With its membership, it includes a variety of videos and resources that are applicable to everyday activites. It also includes recent job hires, great school information, recent events, and various info on national and international competitions.
A great website to buy solos, and ensemble music for a variety of instruments.
A database for a large majority of public domain sheet music avaliable for immediate use/print. This is a great website for all musicians, whether vocal or instrumental.