I just found the web page of this distinguished Dutch bassist who generously posts a wonderful compendium of practice tips and exercises for jazz bassists! Check out Henk Haverhoek's webpage. This looks like the real deal to me. I sent him an email with an appropriate mix of fawning and grovelling (take a look at who all he has played with!) and mentioned that I like to practice arco playing with some trombone etudes like this Bach Arioso, this Bordogni/Rochut Vocalise, or the Galliard Bassoon Sonata #6, page 1 and page 2.

One of my main ideas in starting this blog was to post and exchange practice materials, and Henk is way out in front on this.